Apprentice star and peer Lord Sugar has quit the Labour Party - blaming their "negative business policies" and anti-enterprise approach.
The entrepreneur delivered a damning assessment of the party's business credentials under Ed Miliband's leadership as he revealed he had lost confidence in Labour during the last 12 months.
Lord Sugar, who will continue to serve as an independent crossbench peer, added he made his decision at the start of the year and would have resigned even if Labour had won the election.
He was initially appointed a peer by the previous Labour administration in 2009 but signalled he had sensed a policy shift back towards the principles of "Old Labour" under Mr Miliband - particularly in relation to business.
The peer said he informed the party of his decision on Friday and kept his intentions quiet rather than use them to "possibly damage" Labour's election chances.
But Lord Sugar has made his decision public just days after Labour suffered its most damaging election defeat in a generation.
The party's election campaign under Mr Miliband has also been criticised by party figures in recent days for lacking an economic policy.
The manifesto listed the first task of a Labour government was to change the economy so that it "works for all of Britain's businesses and working people", with policies focusing on zero hours contracts, increasing the minimum wage and cutting rates for small businesses.
In a statement, Lord Sugar said his resignation was accepted as the party had been "aware of my disillusionment for some time".
He said: "In the past year I found myself losing confidence in the party due to their negative business policies and the general anti-enterprise concepts they were considering if they were to be elected.
"I expressed this to the most senior figures in the party several times."
He continued: "By the start of this year, I had made my decision to resign from the party whatever the outcome of the General Election.
"However, I am a loyal person and rather than use my decision to possibly damage the party's chances in the election, I decided, as a relatively high-profile individual, to keep my intentions quiet for the duration of the campaign."
Lord Sugar said he had declined hundreds of media requests to talk about the party's proposed policies, particularly in relation to business.
He said: "I have no wish to stick the boot into the party.
"There are many good people in Labour working hard every day to serve the public and I wish them all the best of luck.
"I am grateful for all the experiences being a member of Labour has brought me."
He added he will continue in the Lords in order to represent the interests of business and enterprise in the UK.
During his maiden speech in the Lords, the peer confronted criticism of his appointment as an "enterprise champion" by Gordon Brown's government.
He also made reference to his successful BBC show, telling peers in 2009: "I am the new boy on the block. In your Lordships' House I am certainly the apprentice.''