The minimum term a babysitter who raped a three-month-old girl must serve under his life sentence was put up from six years to eight by the Court of Appeal yesterday.

But, amid anger at the decision from the baby's family and another victim, the court said that 40-year-old Alan Webster was "so deeply steeped in sexual depravity" that he may never be released from prison.

Lord Phillips, the Lord Chief Justice, who was one of the judges hearing the appeal by the Attorney General, Lord Goldsmith, against the "unduly lenient" tariff, insisted that Webster would remain in jail unless and until the Parole Board was satisfied that he no longer posed a danger to the public. It was "questionable whether that day will ever be reached", he added.

Kirsty Little, who was 17 yesterday, was indecently assaulted by Webster when she was 14. She burst into tears when she heard the decision. "I can't believe the judges have added only two years. It is absolutely ludicrous," she said.

Miss Little, who has waived her right to anonymity, added: "It is disgusting. It is not right at all, especially for that baby. People like him should not be allowed to walk the streets ever again. The court should have set an example, but two more years is no example."

Miss Little, who has suffered nightmares and been prescribed anti-depressants since being assaulted, added: "He is a depraved, sick lunatic. He should be condemned to hell. It horrifies me to think he could be back on the streets. If he ever walks free I will leave the country."

Yesterday's hearing also upheld a five-year sentence on Webster's co-defendant, Tanya French, 20, despite a claim by the Attorney General that it, too, was too low. In accordance with normal practice, time spent in custody awaiting trial is deducted from the sentence imposed.

During submissions to the Court of Appeal last month, Lord Goldsmith said that the sentences did not fit the gravity of the crimes "by a significant margin".

The court declined yesterday to reduce the one-third discount allowed for an early plea of guilty, but said this principle should be reviewed "as a matter of urgency".

Lord Phillips said that Webster had corrupted French when she was 17, the age at which she moved into his home in Hatfield, Herts. French was friendly with the baby's mother and used to babysit for her.

On occasions, the mother allowed French to look after her baby at Webster's home, where the offences took place.

In court, Webster admitted four counts of rape and five indecent assaults. French admitted one rape and four indecent assaults.

Each admitted taking indecent photographs of the other abusing the baby. This was "a course of conduct of horrifying depravity" in which Webster and French used the little girl as a "sex toy".

Webster's assault on the baby was not sufficient to cause internal injuries, and no injuries were noticed by her mother. Experts disagreed on the possible long-term psychiatric damage to the child.

Her mother had suffered "acute distress", the judges added. Finding out about the assaults had been worse for her than an occasion some years earlier when she, herself, had been raped.

In deciding Webster's minimum term following his guilty plea at St Albans Crown Court in January, Judge Baker had taken a "starting point" of 18 years.

Under guidelines, a defendant who pleads guilty at the earliest opportunity is entitled to a discount of one third. That reduced the starting point to 12 years with the possibility of release after six years.

The Court of Appeal decided yesterday that the "extraordinary and abhorrent features" of the treatment of this victim called, in the case of Webster, required a starting point of 24 years.

After taking a third off for his plea of guilty, and halving the sentence as before, Webster was left with a minimum term of eight years.

The baby's family said in a statement after the ruling: "We are in utter disbelief. To say we are disappointed is an understatement.

"There is so much taken into consideration in relation to the rights of the perpetrators, but our ordeal will never be over and the rights of the perpetrators seem to outweigh the rights of the victims."