Tony Blair has been quizzed over the soaring levels of street crime - but has refused to say that the government will meet a commitment to reduce robberies by the end of September.

Speaking during prime minister's questions, Iain Duncan Smith challenged Blair to say by how much recorded street crime had risen over the past 12 months.

Blair conceded that street crime had risen but stressed the government was taking action. "Recorded street crime has indeed risen over the last 12 months," said Blair.

"However, it is as a result of that we are taking the measures, including investing in our police, increasing the number of police on the beat. Even for street crime it would be folly to take that investment out."

Duncan Smith said that crime was now up "30 per cent over the last year and has doubled over the last five years" - and branded the prime minister a failure.

Blair responded: "By the end of September we said we would get street crime under control. I think that he will see from the initiatives that are being taken that we will do that."

The Tories, however, accused the prime minister of rewriting his pledge to avoid a further embarrassing failure. Duncan Smith said that "violent crime is rising, robberies are up" and demanded to know whether the government would stick to its commitment to reduce the number of offences by September.

Blair said the government was not complacent and called on Duncan Smith to support the government's Proceeds of Crime Bill if he was serious about the fight against crime.

Duncan Smith, however, said Blair had committed himself to "reduce street crime to the levels in April by the end of September" but was now backing down on his commitment.

"Would he now like to make that pledge here again?" Duncan Smith asked the prime minister.

"I've just made it a moment ago in the answer I have given," said Blair.

"I said to him that as I indicated before, by the end of September we have to have street crime under control. That is precisely why we are taking the initiatives necessary."

Returning for a further round of questioning, Iain Duncan Smith later challenged the prime minister on previous comments that stock markers were "massively up" since Labour came to power.

He asked the prime minister how "massively up" the stock market was since Labour's 1997 tax on pension funds.

The Conservative leader said the government liked to take responsibility for a rising stock market but "now, strangely enough, its somebody else's fault".

Duncan smith added that European markets were up while British shares were down.

"Does he still believe the pensions tax is still justified by the buoyancy of the stock market?"

The prime minister said he did, and challenged the Tories to say whether they would repeal the tax.

He also pointed to lower interest rates, unemployment and inflation and an absence of "that old Tory theme of boom and bust".