A scheme to pave Oxford's Cornmarket Street with expensive granite slabs, which has already cost £1m, is to be scrapped.

Councillors are considering ripping up the new paving and replacing it with Tarmac.

The move comes after consultants revealed that delivery vehicles were to blame for cracks which appeared in the slabs.

Last summer, the city and county councils paved half the street but by the end of the year cracks had started to appear in the new surface and the £2.2m project was halted.

Work had been due to start again on the paving scheme this summer.

Thicker replacement slabs would have to be used to ensure no further cracking and this could greatly increase the cost of the project. City councillor Colin Cook, executive member for planning, said the most likely option would be replacing the granite slabs with an ordinary road surface like Tarmac.

York stones could still be used to smarten up the street's pavements.

Mr Cook added: "I still want to investigate the possible use of granite but I fear it could prove too costly and the more likely outcome now is taking the cheaper option, because the city council can't afford to spend any more. According to the consultants, the granite slabs could not take the weight of delivery vehicles.

"The whole lot will have to come up, and it may be that work doesn't start again until early next year because we need to meet county council staff first to discuss all the options." John Moyle, managing director of Boswell's department store in Cornmarket Street, said: "This is extremely disappointing, and I hope some work is done in the short term to tidy up the street.

"It will be a shame if what finally appears does not live up to expectations."

Keith Mitchell, leader of the county council, said he was confident neither council could be blamed. He said talks were taking place with the scheme's contractors, engineers, and consultant designers to see who was responsible for the fault.

"We are obviously pursuing any money which the council has spent," he said. "The scheme is worth £2.2m and we need to make sure we either get our money back or a scheme which is worth that amount when it is completed."

Mr Mitchell said the street probably would be tidied up before a final decision was made.

He added that he believed there would be no extra cost "to the public purse".

"My guess is that granite will have to be ruled out," he said.

"I understand that a number of other cities have experienced problems with these schemes.

"They work if they are used by pedestrians but not if vehicles are involved, and it appears that the service vehicles have caused a problem. "I am relieved that we have not gone two years down the line and then discovered a problem and we will now be talking to the city council to discuss the best way forward."

The repaving scheme was launched after Cornmarket Street was pedestrianised following the introduction of the Oxford Transport Strategy in June 1999.