Prime Minister Gordon Brown has written to the Metropolitan Police offering his support for the "fullest possible investigation" into the Labour disguised donations affair.

Mr Brown said he was "ready to assist" the inquiry and had asked Party staff, MPs and peers to "co-operate fully in providing relevant information".

His comments come after the Electoral Commission formally handed over its report on Labour's disguised donations to the Metropolitan Police.

The Commission said in a statement: "The Electoral Commission made the formal handover this afternoon during a meeting with the Metropolitan Police and Crown Prosecution Service (CPS). The police will now review the contents of the report."

Temporary Commander Nigel Mawer will now decide whether to launch a full-scale investigation into the affair - after it emerged that the Government accepted money from businessman David Abrahams through third parties - which is seen as inevitable by MPs.

Scotland Yard confirmed it had received the dossier and a spokesman said: "We will now review the contents of the report."

Earlier, Downing Street insisted it was business as usual for Gordon Brown as it braced for its second police inquiry in two years.

A spokeswoman for Mr Brown said: "The Prime Minister is fully focused on the business of Government and has made clear he is keen that all the issues regarding party political donations are investigated thoroughly."

As rumours swirled of tensions between Mr Brown and Commons leader Harriet Harman, who is also deputy leader of the Labour Party, the spokeswoman insisted: "He's fully supportive of the Leader of the House."

And Ms Harman insisted outside her home that she had not "dropped" Mr Brown in trouble.

She said: "Absolutely not. I strongly maintain that I have complied with the letter and the spirit of the law and I absolutely think that Gordon Brown has absolutely done the same."

Mr Brown was drawn deeper into the scandal after admissions on Thursday that a member of his team had put Ms Harman in touch with one of the go-betweens used by Mr Abrahams, a property developer, to make donations on his behalf.

Ms Harman then received a £5,000 proxy donation but is paying it back.

Assistant Commissioner John Yates, who led the "cash-for-honours" inquiry into the award of peerages by Tony Blair when he was prime minister, will be available to advise the investigation if required.

Justice Secretary Jack Straw, who was Mr Brown's leadership campaign manager, described the situation as "mind-blowing".

It was the disclosure at the weekend that Mr Abrahams gifted Labour £650,000 through a series of associates to get round the law requiring political donors to be declared which prompted the initial inquiry by the Electoral Commission.

Mr Straw also queried the actions of Labour's chief election fundraiser Jon Mendelsohn.

The party's head of election resources said he had written to Mr Abrahams in an attempt to halt the proxy donations, even though he did not alert senior officials or MPs to them.

"The precise state of mind of Mr Mendelsohn and what he then did is a matter for these inquiries," he said.

"But my understanding from what he says is he was concerned. He then decided to take some action in respect of that."

He said that very few people in the Labour Party knew about the situation. He said: "It's not legal and it's not appropriate.

"And it's not just a matter of profound irritation but profound anger to everybody involved in the Labour Party, 99.9 per cent recurring, who are completely straight and upstanding.

"I can't tell you how irritated the rest of us are about this."

He added: "We've got to improve the regulation (of British politics) and this was mind-blowing."

Among Labour backbenchers there was anger and frustration at the difficulties the party found itself in.

"Everybody is infuriated by it," former minister Mark Fisher said. "It is quite extraordinary that we have got ourselves into such a mess. Disastrous in fact. It is quite clear that the public has lost confidence in the Government."

A Populus poll showed 53 per cent of voters agreed that "the Labour Government now appears to be more sleazy than the previous Conservative Government". Only 40 per cent disagreed.

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