Sir James died in 1997 and is now better known for his famous children - Jemima Khan, the writer and activist, and Zac Goldsmith, the Conservative MP - than his business life, which had made him a national figure and billionaire.
And it suggests that Lucan was alive as late as 2000, a year after the Bingham family was granted probate on his estate, the nearest to a legal declaration of his death there has been.
Miss Robey's decision to speak now comes after she gave a partial account under the veil of anonymity to a regional BBC television documentary, when described as "Jill", she outlined how she booked flights for Lucan's elder daughter and son to Africa, where unknown to them they were seen by their father.
The account inevitably created a surge of interest in the enduring Lucan mystery, but elements were contradicted by both George Bingham, Lucan's son, and by Lady Lucan, who said she would have known if it happened - and it did not.
Now Miss Robey, 56, has decided to speak fully in public for two reasons: firstly because she wants her account to be believed, and secondly because she wants to address Lucan's family directly.
She wants them to know that she is speaking with sincerity, and to appreciate the depth of belief among Lucan's friends that the peer was innocent of the murder of the family nanny, Sandra Rivett, at the family home in Belgravia on 7 November 1974.
Miss Robey worked for John Aspinall, the casino and zoo owner who was one of Lucan's closest friends, from 1979 until 1985.
She was the secretary for his casino when she says she twice booked travel for Lucan's children to Africa.
The first time began less than a year after she had begun working when she was asked to come into a meeting in Aspinall's office, with Sir James Goldmsith.
"They were talking about John Bingham," Miss Robey says.
"The conversations were "what are we going to do", "have you been in touch?". I was just making notes - I was asked to take a few notes down.
"At the end of the meeting, John Aspinall was saying "quite definitely, we need to do something about this" and there was a bit of a disagreement between him and Sir James Goldsmith.
"'No we mustn't do anything, causes too much trouble, we just wait," and then the end of that meeting closed with James saying "you speak to him" and it was then said "you only speak to him on that phone don't you?", gesturing to the private phone.
"He [Goldsmith] looked at me, he didn't even know my name, and said what does she know about anything? And Mr Aspinall said she knows a bit, I'm going to bring her in on it."
Miss Robey was already partially aware of the existence in Aspinall's world of Lord Lucan - although he was never referred to by his title, always as John or Lucan, never as "Lucky"', his nickname among the gambling set of friends who bet huge amounts on chemin de fer at the Clermont club, Aspinall's former casino.
That Lucan was alive and In touch with Aspinall after his disappearing in 1974 was widely suspected but never confirmed. But why was Miss Robey not in touch with the police, who had a large group of detectives eager to speak to him?
Firstly, she says, she did not appreciate he was on the run from a murder investigation, and in fact was named as the killer. A coroner's jury in 1975 had returned a verdict - the last of its kind - that Lucan had murdered the nanny.
"When it happened I was totally unaware of it, a lot of things were happening in my life at that time and I had my first child at 19 so was very much absorbed in that. The last thing I would look at would be scandalous news," she says.
When working for Aspinall, she says, she realised Lucan was involved in something wrong: "I knew he was hiding, I knew he was in Africa, I knew we were hushing it up. I knew he'd fallen out with his wife and I knew it was a major secret but for whatever reason I didn't appreciate there had been a murder until some years later.
"It didn't occur to me to be honest. I had a very great deal of admiration and respect for him [Aspinall] and it just didn't occur to me that he would get me into any kind of trouble.
"I thought maybe he gambled all his estate away or something that, maybe he'd stolen money, I'd had it in my head that it was all to do with money. And the fact that he was wanted by the police would indicate that it must be embezzlement or fraud or something.
"If I had have known it was a murder, I think I would have handled things quite differently. In fact I know I would have done."
Aspinall was careful to emphasise the need for secrecy after the meeting, taking her into his office a couple of weeks later to say how important it was.
"He said: 'what do you know about Lucan?' I said 'nothing really', he's got Into some sort of trouble I understand and is on he run and it was sort of yes, that'll do."
Within a few days she heard Aspinall on the phone saying "yes I'll do it, yes I'll do it", to a person he said was Lucan.
After that she attended another meeting with Goldmsith, in which a phonecall was made to Lucan.
Goldsmith asked Aspinall "have you spoken to him?" and Aspinall replied "Yes, we've talked", but there was an argument - "slightly raised voices" Miss Robey says - with Sir James saying "It's too risky".
It was then a call was made to Lucan. Aspinall asked: "Can you wait?", then said to Goldsmith: "No he's not waiting, if he has to wait, he's coming back."
"James Goldmsith said: 'OK then. Do what you have to do'," Miss Robey recalls.
The plan went ahead. Frances, then 14, and George, due to celebrate his 13th birthday that September - "I remember thinking, he's almost a teenager" - were to go to Gabon.
The plans were meticulous.
Second passports were obtained to avoid a record appearing on their first ones, and a chauffeur was organised to take them to the airport to fly Air France to Libreville, the capital of Gabon, then upcountry to Franceville, where Aspinall had a centre caring for young gorillas orphaned by hunters. After that they were to fly to Treetops, the safari resort in Kenya, then home.
Lucan's youngest daughter Camilla, then 11, could not go, because she had no passport - her name was in her mother's - which made obtaining a second impossible.
There was one detail which Miss Robey knew well as it had been discussed at the meeting: on no account could the children know their father had seen them. They were wards o
f court and had been since before their father's disappearance, but legal steps were under way for Bill Shand Kydd, the jockey and Lucan's brother in law, to become their guardian and they could not be jeopardised. It was never said that Mr Shand Kydd so much as knew of the plan.
Aspinall had told Goldsmith in the meeting: "It won't be a problem. They won't recognise them, he won't make himself known to them, nobody will be aware of that."
The trip apparently went to plan: little was said, other than that "Mr Aspinall was pleased with it" and the next year, this time at the Easter holidays, the arrangement was repeated.
"I remember I booked flights. It was the same deal, second passports, flights, pick them up from school early, that sort of thing," she says, and again it was clear that things had gone well.
There was no other trip, to Miss Robey's knowledge, and in 1985 she left Aspinall's casino to have her second daughter.
Before leaving she had "small conversations" with Aspinall about Lucan - he once said "everything went well then didn't it" in reference to the Gabon trips - then a final meeting as an employee in which he emphasised the need for secrecy.
"He just said you know I trust you," she says.
But he also gave her a code so that she would know what had happened to Lucan: as long as Aspinall publicly said that Lucan was guilty of murder and had committed suicide after it, she would know that Lucan was alive.
"He told me that there would come a time when Lord Lucan would pass away and at that point he would give a message through the press and I would know that it was OK to speak," she says. The message would be that Aspinall would change his public view.
There was sporadic contact - two meetings, a handful of phone calls - but that petered out as her family - she has three children, now all adults - took priority.
Aspinall died in 2000 and a few years later, in the aftermath of surgery, Miss Robey became increasingly interested in the past. Discovering first that her old employer was dead, she started looking at his life, and then the Lucan mystery, coming across clips from a documentary in which George Bingham spoke of his father and his desire to clear his name.
"I just immediately thought I can tell him something, I can sort of tell him what I know and it can sort of help him piece things together," she says.
"He seemed to be genuinely looking for answers."
She felt that she wanted George Bingham to know something she had seen first hand: Aspinall's utter belief that his father was innocent.
Aspinall had been a loyal employer, a man who had been kind and considerate to Miss Robey and her colleagues. He had also been straightforward, she says, in criticising Lucan for running away.
"In the beginning when he spoke about it, he had a lot of criticism of what John Bingham was trying to achieve but he genuinely - I would say one hundred per cent - considered him innocent," she says.
"I'm not saying, and I can't say, whether he would have covered up for him if he thought he was guilty but I think he's made of better stuff than that.
"He had certainly made it clear to me that he believed he [Lucan] was innocent of whatever he was accused of. He just agreed wholeheartedly as did Sir James Goldsmith to stand by him and support him. I think he genuinely believed a mistake had been made, he was innocent, and he was doing the best he could to help him."
She also found Aspinall's final interview, with the Sunday Telegraph in 2000, in which he repeated his view that "he had botched it" and ended his life - which meant, Miss Robey says, that Lucan was alive in 2000.
Keen to speak to George Bingham, she tried to contact him but the effort was unsuccessful and a letter written to his London club was unacknowledged.
Last year she contacted the police and told them everything she recalled, although it seemed less dramatic to the officers she spoke to than to her: "They said to me everything you've said, we're already aware of."
Still hoping to contact the Binghams, in February she gave an interview as "Jill" to Inside Out, the regional BBC documentary series, telling some of the part she played.
Miss Robey had hoped that speaking out would encourage George Bingham to get in touch. Instead he made a public statement which said he and his siblings had been on safari to Kenya, but much later, in 1985.
"Both my sisters were present as were two other families, neither of which had any connections to John Aspinall," he said.
"The airline tickets, safari expenses and hotels, as regards myself, were paid for by my family trust."
He added: "I have not, to the best of my knowledge, seen my father since November 1974."
His mother Veronica, Lady Lucan, made a rare public statement which contradicted Miss Robey's account and said: "It's rubbish, I can guarantee they didn't go to Africa. It's ridiculous, it's false.
"I was their carer, I would have known if they had gone to Africa. I had to get permission from the court to take them abroad or even into the country. I never took them abroad."
For Miss Robey the response of the family meant her hopes of establishing a rapport with them and communicating privately were over.
Additionally being anonymous had meant people questioned her motive for speaking and now she goes public today to make clear that she is neither a fantasist, a busybody, or someone motivated by financial gain; she has not been paid for this interview or that with the BBC.
Instead she says she wants to convince the Bingham children that Aspinall was genuinely loyal to their father and convinced he was innocent. Why else, she reasons, would he have organised the two trips for Lucan to see his children? They should also know their father was alive in 2000 - and most importantly of all, that he loved him.
She knows that at this distance her account cannot be independently verified. Goldsmith is dead, and Mr Shand Kydd, now 75, maintains a silence on the Lucan affair, which this weekend he would not break.
"I feel quite content now that George Bingham does not want to speak with me and I fully respect that decision," she says.
Instead she has a public message for him: "I want to tell him his father was alive and his father certainly absolutely did love his children.
"Everything that was done was based on them, and the thing that I was going to tell him, was that certainly John Aspinall and James Goldsmith believed in his father's innocence.
"I considered it a good thing to try and allow a father to see his children, who clearly meant so much to him that he was prepared to risk his own freedom."
It is a simple message and now that it is delivered, Miss Robey is determined to return to her life in France where she now lives.
It may be her last word; but it is unlikely to be the last word on the mystery of Lord Lucan.
