The tax credit row which has seen Oxfordshire families overpaid £13.1m reached Westminster yesterday with Tory leader David Cameron saying his Witney surgeries are full of people who have been told to repay the money.

Speaking during Prime Minister's Questions, Mr Cameron blamed Chancellor Gordon Brown for the "mess", which has seen millions of households in the country overpaid by £2bn in each of the past two years.

In Oxfordshire, 16,000 claims made by families for 2004/5 were overpaid to the tune of £13.1m an average of £825 each.

Mr Cameron said: "All of our surgeries are full of cases who are victims of incompetence.

"The Chancellor designed and administered the tax credits system, yet he hasn't made a single statement on tax credits in the last year.

"Ministers create a massive bureaucracy that becomes a painful paperchase for hardworking families so why do they refuse to take responsibility when it all goes wrong?"

Mr Cameron said in each of the last two years almost two million households had been overpaid and the money was now being "painfully clawed back".

But Prime Minister Tony Blair responded that he was proud of the role played by tax credits in lifting families out of poverty. He said: "Tax credits provide support to some 20 million people in this country, including six million families and 10 million children."

His comments followed the publication of a damning report by MPs into the "appalling" overpayment of tax credits to poor families.

The House of Commons Treasury Committee concluded that "too many low-income families have been wrongly paid and messed around".

The report called for claimants to be allowed to appeal to an independent tribunal against attempts by tax officers to claw back overpayments. Last week, the Oxford Mail reported that 16,000 Oxfordshire families were overpaid hundreds of pounds following a second year of administrative blunders. A further 7,400 claimants were underpaid leaving them £4.8m out of pocket.

Andrew Smith, Labour MP for Oxford East, said he was receiving a "steady stream" of constituents worried about having to repay overpaid credits.

He said: "It shouldn't be necessary for people to go to their MP to sort this out. I have made representations to Gordon Brown to make the system simpler and more straightforward."

It has also emerged that HM Revenue and Customs had written off "substantial sums" after it had accepted responsibility for administrative errors. The Child Poverty Action Group has warned that families who face having to pay back credits are often left "struggling to survive".