NICK Clegg was last night urged to hand back the Liberal Democrats' "dodgy donation" of £2.4 million by Scottish conman Michael Brown.

The move follows pressure on the Conservatives to return the so-called tainted money they received from jailed swindler Asil Nadir.

Simon Danczuk, Labour MP for Rochdale, who has been urging David Cameron to hand back the £440,000 donated by Nadir's Polly Peck business in the 1980s, said the LibDem leader should do likewise in the case of Brown.

"The same principle should be applied to the Liberal Democrats," Mr Danczuk told The Herald. "They should stop refusing to give the money back and do the decent thing and hand back the £2.4m that Michael Brown gave them."

He added: "Nick Clegg says he wants to clean up politics, but no-one will take him seriously until he returns the dodgy donation from Michael Brown."

Brown, from Glasgow, was convicted in his absence in November 2008 of stealing £5.2m after posing as a bond dealer who had connections to royalty.

He had been on the run for nearly four years before he was tracked down to the Dominican Republic and the exclusive resort of Punta Cana.

He was living there with his dog, Charlie – named after the former LibDem leader Charles Kennedy. Brown began a seven-year jail term in May on his return to Britain.

The 46-year-old fraudster donated £2.4m to the LibDems ahead of the 2005 General Election, the largest gift the party has ever received.

It was given by Brown's company, 5th Avenue Partners, and funded with investors' money. Among the clients defrauded was Malcolm Edwards, former chairman of Manchester United. He lost £6m.

The Electoral Commission, the donations watchdog, looked into the Brown donation and concluded the LibDems could not be blamed for taking the money, having accepted it in good faith.

A party spokeswoman said: "The commission inquiry in 2009 found the party accepted the donation in good faith and were in no way at fault.

"It cleared the party of all wrongdoing and accepted at the time of the donation, 5th Avenue Partners Ltd was a permitted donor."

However, the threat Mr Clegg might be forced to give back the £2.4m has been resurrected.

It has emerged the office of the Parliamentary Ombudsman is investigating a complaint that the commission did not act appropriately and failed to undertake its "statutory function to exercise its discretion reasonably in respect of donations to a political party".

It said it was investigating "a complaint made by a member of the public about the Electoral Commission's investigation into donations in the name of 5th Avenue Partners Ltd to the LibDems.

"The Deputy Ombudsman, Kathryn Hudson, is leading the investigation".

The agency's spokeswoman said she could give no indication as to how long the investigation would last, but said this was a "complex" case and could take several months to conclude.

If Ms Hudson were to find against the commission, then political pressure on Mr Clegg to hand back the £2.4m donation would increase greatly.

Meanwhile, pressure continues to build on the Prime Minister to hand back Nadir's donation.

Lord McAlpine, Tory treasurer at the time of the gift, has insisted Mr Cameron had a "moral duty" to return the money after the former fugitive tycoon was jailed for 10 years this week for stealing £28.8m from the global business.