In a "doomsday scenario" he hoped the force would not lose more than 500 officers out of its current strength of more than 31,000.
The cuts in London reflect a similar pattern across the country with 264 public counters expected to close by Chief Constables as they try to balance their budgets against a backdrop of steep spending cuts.
In some parts of the country, such as Essex, Surrey, Cumbria, Gwent and Kent, police forces have set up mobile police stations in car parks.
Forces across the country have to find £2.4 billion from their budgets and it is this which has made police stations vulnerable.
In addition to the closure of the counters another 179 buildings, which already have no public access will be sold off.
Paul McKeever, chairman police federation: "A great many police stations are closing down in London and all over the country. It's like lowering the flag of the criminal justice system in the community.
"But at the same time forces are facing spending cuts of 20 per cent and are struggling to make ends meet so they are having to look forward to innovative solutions.
"I look forward to discussing them with Stephen Greenhalgh in the next few weeks."