The prime minister's official spokesman dismissed as "contemptible" suggestions that Mr Mandelson deliberately delayed starting repair work on the flat for two months over the summer until his return to the cabinet at the last reshuffle.

As Northern Ireland secretary, his private home would normally be fitted with bullet-proof windows and other security features - the work being paid for by the government.

In the weeks leading up to the last government reshuffle, most speculation had centred on whether Mr Mandelson would be brought back into the cabinet following his resignation last Christmas.

He had stood down as trade and industry secretary, along with then-paymaster general Geoffrey Robinson, after it was disclosed Mr Mandelson had accepted a secret loan of £373,000 to buy a Notting Hill house.

He subsequently sold the house and repaid the loan, buying the flat now being refurbished in the same area.

'Fishy smell'

The house Peter Mandelson had to sell following disclosure he secretly borrowed £373,000 from Geoffrey Robinson

Tory former Home Office minister David Maclean said on Monday he would be tabling a series of Commons questions in an attempt to find out whether Mr Mandelson had delayed carrying out renovation work on the flat on purpose, so that it could be done by the government at the same time.

When Mr Mandelson bought the flat in the summer it was reported to be badly run-down and in need of extensive work before it could be fit to live in.

But according to The Daily Mail newspaper, repair work did not start on the property until October - after Mr Mandelson had returned to office.

The Northern Ireland Office has refused to disclose details of the work being carried out, citing its policy of never discussing such security matters.

However Mr Maclean said Mr Mandelson should now make clear whether he knew in the summer that he would be getting the Northern Ireland job and had held back from renovating his new flat until he was back in government.

"I am trying to get to the bottom of why he didn't start the refurbishment earlier. It just seems to be a bit odd - the coincidence of timing," said Mr Hunt.