An unusual £600,000 donation has been handed to 30 Labour and 15 left of centre Liberal Democrat election candidates by a former Lib Dem peer in an attempt to create an Ed Miliband-led progressive government.

The money has been provided by Lord Oakeshott, a wealthy peer, who resigned from the Lib Dems in May after warning that the party was “heading for disaster” under Nick Clegg’s leadership.

Oakeshott, now an independent, described his donations as “doing his bit to save our country from a Tory government cringing to Ukip”. The peer also disclosed he has given a further £10,000 for the campaign to re-elect Caroline Lucas, the Green MP in Brighton.

The donations were given discreetly over the last two months but, due to be made public in the normal way by the Electoral Commission shortly, are also intended to encourage voters to think, vote tactically and elect a reforming parliament with a “Labour-led government headed by Ed Miliband as prime minister”.

Oakeshott, once a close political ally of the business secretary, Vince Cable, has distributed his money equally between Lib Dems and Labour. The Lib Dem tranche has gone to the campaigns of eight MPs and seven candidates in marginal seats. Oakeshott has clearly backed those Lib Dem candidates he hopes are probably more likely to want to go into coalition with Labour than the Tories, but he stresses his donation has been entirely unconditional.

He said: “All of them are robust, progressive, rooted Lib Dems, with whom I was or would have been proud to sit and vote in parliament.” The seven sitting Liberal Democrat MPs to whom he has given cash are Norman Baker, Lorely Burt, Tessa Munt, John Pugh, Martin Horwood, Adrian Sanders and Jenny Willott – all, he believes, need support to win.

Oakeshott gave £10,000 each to 30 Labour candidates in marginal seats across the Labour political spectrum. Twenty-nine are attacking Tory marginals with small majorities and one, Melanie Onn, is fighting to hold Great Grimsby for Labour against Ukip. He added: “There are of course, many more Labour than Liberal Democrat candidates in winnable marginal seats, so I’ve had to concentrate my cash on first-time Labour candidates, rather than ex-MPs.”

The Labour candidates include those in Carlisle, Hastings and Rye, Hove, and Brighton Kempton in the south; Gloucester and Kingswood in the west; and Great Yarmouth and Peterborough in the east. Miliband was made aware of the donations.

Oakeshott believes the Tories are outspending progressive candidates, and believes the appetite for anti-Tory tactical voting remains strong, especially since so much of the polling by Lord Ashcroft in key marginals can be used to guide voters how to vote tactically.

Oakeshott resigned the party whip after funding opinion polls in Lib-Dem-held seats showing how the party was in danger of losing a raft of MPs, including Clegg’s own seat. Oakeshott clearly hoped the polls might prompt a coup against Clegg, but the revolt fizzled out.

Oakeshott said: “Britain stands on the edge of a cliff with the general election only 105 days away. Will we vote Tory or Ukip for Euro referendum chaos, lasting two years at least and putting thousands of businesses, millions of jobs and our long-term peace and security at risk?

“Or will Labour, Liberal Democrat, Green and all progressive voters come together in the marginal seats that matter to elect a parliament for progress and reform and a Labour-led government with Ed Miliband as prime minister?

“He has stood firm against the clamour for a referendum with considerable courage and nous. Scotland shows how referenda, even with 55-45 vote, can settle nothing, just open a can of worms.”

He added his spending would only do something to redress the spending imbalance saying that many Lib Dem and Labour candidates had told him that the Tories have “spent over £100,000 campaigning against them, even before the official election campaign – and spending limits – started in December”.

A property investor who began his City career at Warburg before a spell running the pension fund at Courtaulds, Oakeshott runs his own business OLIM Property managing commercial property portfolios for pension funds, investment trusts and charities.