Lord Oakeshott returns to Lords following Nick Clegg 'coup' scandal
The peer, formerly a Liberal Democrat, commissioned a number of polls which suggested the party was facing wipeout at the general election.
After it was revealed he shared the results only with then business secretary Sir Vince Cable, Lord Oakeshott resigned from the party and took leave of absence from the upper chamber.
But today he tweeted that he had re-joined peers as a non-affiliated member to campaign for Britain to remain in the European Union.
"I've rejoined Lords to help keep Britain in Europe. We won 1975 Referendum with vision of prosperity, progress and peace. Still @Stronger_In," he wrote.
The peer had shared his polls with Sir Vince “several weeks” before they were leaked to the press.
Then Lib Dem leader Nick Clegg confirmed he had not been informed about the surveys by either the peer or the member for Twickenham.
Lord Oakeshott commissioned the polls in four key areas, including Mr Clegg’s seat of Sheffield Hallam.
In his resignation letter from the party, Lord Oakeshott said: "I am today taking leave of absence from the House of Lords and resigning as a member of the Liberal Democrats.
"I am sure the party is heading for disaster if it keeps Nick Clegg; and I must not get in the way of the many brave Liberal Democrats fighting for change.
"I leave, with a heavy heart, the party I helped to found with such high hopes with Roy Jenkins, Bill Rodgers, Shirley Williams and David Owen at Limehouse in 1981.
"We then, like most Liberal Democrats now, wanted a radical progressive party, not a 'split the difference' Centre Party, with, in Shirley’s memorable words, no roots, no principles and no values. But that is where Nick Clegg has led us.”
He added he was “sorry I have so upset and embarrassed my old friend Vince Cable”.