One in five members of the Liberal Democrats quit the party last year, with the worst losses in constituencies represented by government ministers, as disaffected activists walked out in protest at the coalition.

An investigation by The Independent on Sunday reveals the Lib Dems' collapse in support in the polls has been matched by a desertion of thousands of members. The exodus – far worse than the usual post-election drop-off – threatens to undermine the party's support base. Officials in one minister's constituency reported "members and supporters not being willing to campaign for the party".

The loss of thousands of members will leave a hole in the party's finances. To join the Lib Dems costs a minimum of £12 a year, or £6 for students, under-25s and those on benefits. The financial accounts of all local parties with an income of more than £25,000 paint a grim picture for the Lib Dems.

Membership of the Scottish Liberal Democrats has shrunk by 26 per cent. Craig Harrow, convenor of the party, said campaign teams were "devastated" by last year's results in the Holyrood elections, with MSPs "swept from office on a tsunami for the SNP".

The trebling of university tuition fees to £9,000 appears to have hit the party particularly hard, with Liberal Youth, the party's student wing, seeing more than half its 6,000 members quit in 2011.

Over the same period, Labour Students rose eight per cent to 6,782. Among nine Labour constituency parties to report, there was a net drop of just one per cent. Labour said it will not comment on national membership figures until they are published later this year. A survey of 100 Conservative associations reveals an average drop of seven per cent of members in the last 12 months. David Cameron's Witney constituency reported a two per cent rise.

Senior Lib Dems had hoped that entering the coalition would persuade voters they were a credible party of government, but ministers' constituencies have suffered some of the steepest losses in support. The treasurer's report in Somerton and Frome, where minister David Heath is MP, stated that in some areas "there was very little canvassing due to members and supporters not being willing to campaign for the party". The party lost "key campaigners who disagree with coalition politics and they were missed".

Argyle and Bute, where Alan Reid is MP, reported "a dispiriting year", while in Newcastle there was "a tough situation on the doorstep... due in part to the national economic situation and our party's part in the coalition". Across six regions – East of England, North West, Scotland, South Central, Western Counties and Yorkshire & Humber – there was a drop of 7,693 members in a year, or 23 per cent. Details were not released in other regions.

A Lib Dem spokesman said: "We have never hidden from the fact that our decision to put national interest first and our own party interest aside in order to form a coalition would be difficult. We pay tribute to those members who've stuck it out, braved the doorsteps and stuck with the party. They are the heroes of liberalism and we salute them every day."

At least 21 Tory associations gained members in the last year, though some ministers saw a fall, including Andrew Lansley, down 28 per cent, Philip Hammond, down 24 per cent and Theresa May, whose constituency lost 20 per cent. The party said it had launched initiatives to "attract new members and reconnect with lapsed members".

Additional reporting by Gregor Cubie and Hannah Todd

Falling membership

David Heath The deputy leader of the Commons clung on to his Somerton and Frome seat, but has lost 27 per cent of members who disagree with coalition politics.

Sarah Teather The largest drop in membership came in the Children's Minister's local party in Brent. It saw 42 per cent of activists quit in the space of 12 months.

Nick Clegg The embattled deputy PM and Lib Dem leader saw an 18 per cent drop in membership in his Sheffield Hallam constituency, despite efforts to "build support for the party".

Lynne Featherstone The number of Lib Dem members in Hornsey & Wood Green, represented by the equalities minister, dropped 21 per cent to stand at below 300.