How much does it cost to win a vote? £1.54 if it's for the Tories

The Conservatives outspent all the other parties combined on this year's general election, figures released by the Electoral Commission reveal.

The biggest change from the previous election was the dramatic depletion of the Labour campaign's war chest. It spent just over £8m on the three month campaign, less than half the £16.7m spent by the Tories. The figure for the Liberal Democrats was £4.8m, the most they have ever spent.

The Conservatives were so rich that one day they spent £5,532 projecting a picture of David Cameron onto London's Battersea Power Station.

They also invested thousands of pounds in ideas that were dropped before the public had even heard about them. M&S Saatchi billed them £3,466 for a poster to warn the public about the pitfalls of a hung Parliament.

There were also bills of more than £2,500 for ideas featuring a "double-headed donkey" – a reference to a famous cartoon by David Low ridiculing the Coalition Government of 1922.

The figures also reveal the problems Labour had attracting wealthy donors after Gordon Brown replaced Tony Blair as leader. In 2005 they were in a position to splash out £18m.

Among the items listed on the Tory campaign's returns are £140,000 worth of prizes for fund-raising auctions donated by the restaurateur Richard Caring, who was previously a Labour donor.

One embarrassment for Labour, which the Tories were quick to point out yesterday, is that bills for more than £35,000 for the use of ministerial cars during the campaign still have not been paid, after the legal deadline has passed.

But Labour countered that it was not their fault. A source at the party's HQ said civil servants sent the bill to Downing Street – apparently forgetting that Labour is no longer in power – so the invoices did not reach Labour until the deadline had been missed.

But at least the Labour Party can claim to have got better value for money, because each vote they gathered cost them an average of 93p, whereas the high-spending Tories gathered only one vote for every £1.54 they spent. The Lib Dems did even better, spending 70p per vote gained.

One item that did not go to waste was the £4,524 they spent on a bespoke pair of 5ft-high boots, which were used for a photo shoot that purported to show Gordon Brown crushing the economic recovery.

They also spent £188 on a mask of Tony Blair and more than £600 on Gordon Brown masks.

The Labour Party's campaign returns reveal that David Prescott, son of the former Deputy Prime Minister, was paid £17,500 in consultancy fees – £250 a day – for accompanying his father around the country on the "Go Fourth" campaign. This was on top of hotel bills and other costs.

Labour spent more than £1,600 on gas and inflator equipment for campaign balloons and £351 on six boxes of 60 bars of rock with the campaign slogan "A Future Fair for All" running through them.

Another £360 went on hiring a Mercedes S class limousine for a day for Alastair Campbell, who was also put up at Labour's expense for one night in a £340 hotel room. Everyone else in the Labour campaign team, apart from Gordon Brown, had to settle for a £118-a-night room that night.

One of the biggest items of expenditure for the Liberal Democrats was the £253,000 they were charged for private flights for Nick Clegg, Vice Cable and other senior party members. Maintaining Mr Clegg's website during the campaign cost more than £10,000.

Of the other parties, the biggest roller by far was the UK Independence Party, which spent £732,780 but won no seats. The Green Party invested £325,425, most of which went on the successful campaign to see Caroline Lucas elected as the first Green MP. The Scottish National Party spent £315,776, Plaid Cymru £144,933 and the BNP £29,460.