Public transport: Cameron accused of betrayal after older people face wait for bus passes

Government sources insisted it was "extremely unlikely" the proposal to bring forward the raising of the qualification age from 60 to 65 would actually be implemented.

But Labour said Ministers must now "come clean" and explain exactly what their plans were for concessionary bus travel.

Under the previous Labour government, the age at which both male and female pensioners are entitled to free bus passes was due to increase in line with the female retirement age, reaching 65 in 2020.

However, under one option for spending cuts drawn up by the Department for Transport (DfT), that process could be speeded up.

Like most Whitehall departments, the DfT has been instructed to come up with proposals for budget cuts of 25 per cent and 40 per cent over the next four years.

They will then form the basis of the negotiations between the Treasury and the departments leading to the spending review in the autumn.

It is understood that the DfT's 40 per cent plan includes a proposal to bring forward the raising of the eligibility age for free bus passes.

The issue is particularly sensitive for Mr Cameron as during the General Election campaign he dismissed Labour claims that the Conservatives would slash free bus travel as "lies".

Downing Street sources insisted that they were not going back on the commitment. "The Prime Minister's pledge stands," one source said.

The Prime Minister's official spokesman said that the Government was committed to protecting free bus travel for the elderly in line with the coalition agreement between the Conservatives and the Liberal Democrats.

"The position is as set out in the coalition agreement. We are committed to protecting free bus travel for older people," the spokesman said.

However shadow Transport Secretary Sadiq Khan accused Mr Cameron of betraying his election promises.

"David Cameron owes the public an apology today. His mock outrage during the General Election campaign has been shown up as a cynical and misleading act, and his manifesto commitment to protecting concessionary fares as a sham," he said.

Deputy Prime Minister Nick Clegg was asked if the bus pass scheme was safe as he took questions following a speech in London.

Mr Clegg said: "We are not going to scrap free bus passes, but clearly we are going to review how it operates.

"It is far, far too early to suggest that we are going to do one thing or another, because this is all the kind of thing we are going to have to look at in the round."