The Nationalist administration was in growing political trouble last night after Alex Salmond refused repeatedly to give long-term guarantees for key elements of concessionary bus passes for the over-60s.

Although the First Minister categorically promised MSPs that he would not raise the age threshold for the passes from 60 to 65, he was less forthcoming on whether his government would be likely to make any changes to rules governing routes, time of operation and distances.

His spokesman was equally reticent, saying later that there were no plans to change these elements, but refusing to give an outright guarantee that they would remain as they were.

The concessionary fares scheme for senior citizens and disabled people has been one of the most popular benefits of devolution since it was introduced by the previous Labour/Liberal Democrat Executive in April 2006. More than one million Scots have concessionary travel cards, an estimated take-up of more than 90 per cent.

The Times reported this week that SNP ministers planned to review the scheme and that, according to a written answer from Stewart Stevenson, the Transport Minister, the budget allocation for it would fall in real terms, from £189.4million to £179.4million in 2010-11.

Labour and the Liberal Democrats say that any reduction in funding throws up the prospect of major changes. Speculation is rife in Holyrood that ministers will cut the hours between which people can use their pass, or reduce the distances they can travel.

The SNP claims that plans for the review had, in any case, been put in place by the previous administration and that far from reducing the cash available, ministers were increasing it by £10million by switching money from a similar scheme for young people that has had a lower-than-expected take-up.

It is known that bus companies operating the scheme are worried that the support they receive from the Scottish government will soon fail to cover the recent increases in fuel duty and the costs of accommodating the number of card-holders. There are other concerns that any funding gap will be covered by a fares increase for bus passengers who are under 60.

Many at Holyrood were surprised that Mr Salmond did not take the opportunity to lay to rest fears about the future of the scheme during First Minister's Questions yesterday. Wendy Alexander, the Labour leader, challenged him to guarantee there would be no change to the time of day when pensioners could travel, the distance they could travel or the number of journeys that could be taken.

Mr Salmond did not answer the question directly but replied: “The one difference between this administration and the last one is that the Transport Minister has already said we are not changing the eligibility for old people and disabled people.

“Will Wendy Alexander stop scaremongering? The old people of Scotland have trust in the Scottish National Party. It's not even our review - we are carrying forward what the last government said they were going to do two years ago.”

Pressed again on the issue of the future scope of the concessionary fares scheme, Mr Salmond said: “The Scottish government has no plans whatsoever to increase the qualifying age for concessionary fares on buses, we'll not be considering this as part of the review.”

The First Minister also refused to say when the criteria for the review would be made public. His spokesman said later that the aim of the review was to see whether the scheme could be improved.

“We are in negotiation with the bus companies at the present time. There is a lot of public money going into this and we want to make sure we get the maximum benefit for the travelling public,” he said.

He was unable to say when the review criteria would be published and stuck to the line that there were “no plans” to change the way that the scheme operated. Asked to give a guarantee that it would not change after the review, he repeated: “There are no plans to make changes.”

Ms Alexander said that pensioners had cause to be concerned. “It is clear the First Minister is refusing to guarantee the current access enjoyed by Scotland's pensioners to free bus travel,” she said.

The Scottish Conservatives said that while Mr Salmond had been very quick to rule out any changes on eligibility, he was very slow to comment on possible changes in services. Alex Johnstone, the party's transport spokesman, said: “We have all heard the phrase ‘no plans' before. It does not close this issue down.”

Alison McInnes, of the Lib Dems, said that passengers should not have to pay for the SNP's “inadequate” funding for the scheme. “As the budget stands, from next year operators will be providing concessionary travel but they are unlikely to receive full reimbursement. The most likely consequence of this is further fare increases for paying passengers.”

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