Pensioners have taken more than 700,000 extra free trips on Oxford buses in the past six months — leaving the city council with a £400,000 budget black hole.

A scheme allowing pensioners to travel anywhere on local services free of charge and changes to how councils pay bus operators has seen an increase of almost 50 per cent in the number of subsidised journeys.

It is costing the council hundreds of thousands of pounds and has led to overcrowding on some routes.

Council executive member Antonia Bance lobbied local government minister John Healey for extra money to cover the cost of concessionary journeys into Oxford, at last month's Labour Party conference.

She said: "This is going to mean a very difficult budget and some belt-tightening across the service.

"With rising fuel costs, we're entering a difficult time but we're determined to meet these challenges without impacting on the most vulnerable."

In the first six months of the new scheme, the council has subsidised about 2.2m journeys made by pensioners into Oxford, and this will push the council £400,000 over its subsidy budget by the end of the financial year. The previous year, there were 722,000 fewer journeys.

Ms Bance added: "We have had some grant funding from the Government but there's an obvious shortfall and we need to see an adjustment.

"Cities like Reading, Brighton and Cambridge, with large rural hinterlands, are in a similar position and after lobbying Mr Healey I sent him a letter, which will add to the voices expressing concern.

"We have done our best to point out that there's a serious problem here."

Ed Turner, deputy leader of the council, added: "It's absolutely brilliant that so many pensioners are using the buses but it's putting us under severe financial strain and that's why we're lobbying for a fairer financial settlement — we need better compensation from the Government."

The council has budgeted £2m to pay for the scheme but is only getting an £800,000 Government grant.

Stagecoach buses spokesman Chris Child said: "There has been some overcrowding on certain routes, in particular the No 10 service, from Oxford to the John Radcliffe Hospital, where there's high use of concessionary fares.

"There are pinch points, but we're coping and looking to put in extra capacity where it's needed."

Louisa Weeks, operations director of the Oxford Bus Company, said: "We have managed to cope with the increase in concessionary pass users."