GORDON Brown has waded into the row over Shadow Chancellor George Osborne's discussions with a Russian billionaire over a donation to Tory Party funds - calling for the authorities to investigate.

Mr Brown told MPs he regarded it as a `very serious matter indeed'.

"I hope that it is investigated by the authorities," he said.

Tory officials said that Mr Brown needed to explain what allegations he wanted investigated, and by whom, since no allegations of any offence had been made.

The Electoral Commission, meanwhile, reaffirmed that it had not seen any evidence an offence had been committed under party-funding laws.

Pressure

Tatton MP Mr Osborne was under intense pressure after his account of discussions concerning a potential donation from Oleg Deripaska was contradicted by witnesses.

He has refuted claims by banker Nathaniel Rothschild that he had sought a £50,000 donation.

But Mr Rothschild, a Tory-supporting university friend of Mr Osborne, maintained the Conservatives had been interested in pursuing a donation. He insisted that the subject came up in conversation three times in one day.

To add to the pressure, former party chairman Lord Tebbit became the first senior Tory Party figure to publicly criticise Mr Osborne, saying he had behaved unwisely and adding: "One has to say that George Osborne should remember that those who sleep with dogs will get fleas."

Illegal

Mr Osborne has admitted meeting the Russian tycoon four times in a week, but denied seeking a donation.

It would have been illegal for Mr Deripaska, an aluminium magnate reputed to be Russia's richest man, to donate to a British party as he is not on the electoral register. But there was mention of Leyland DAF, a British-based firm owned by Mr Deripaska, which could have legally made a donation.

Tory leader David Cameron has backed Mr Osborne and challenged Business Secretary Lord Mandelson, who was also present at some of the gatherings in Corfu, to provide a similar account of his discussions.

The row was triggered when Mr Rothschild wrote a letter to The Times saying Mr Osborne and Tory fundraiser Andrew Feldman spent time on Mr Deripaska's yacht off Corfu, and claimed they tried to `solicit a donation' from him.

In their statement, Mr Osborne and Mr Feldman said: "At no point did Mr Osborne or Mr Feldman solicit or ask for a donation, suggest ways of channelling a donation or express any wish to meet with Mr Deripaska to discuss donations."