For 29 MPs, opposition to scrapping the first-past-the-post voting system is a matter of raw political survival, an analysis by The Independent has found.

Eight Labour MPs and 21 Tories campaigning against the alternative vote would not have been elected in last year's general election had AV been in operation. They include the Tory MP George Eustice, one of the key spokesmen for the No to AV campaign, who won his Camborne and Redruth seat with barely 38 per cent support.

Researchers at Essex University, who analysed every constituency, suggested that the Tories would still have been the largest party at the last election under AV. But the Commons would have looked significantly different: David Cameron's forces would have won overall 23 fewer seats; Labour would have had 10 fewer MPs; and the Liberal Democrats' ranks would have been bolstered by 32 extra MPs.

Among the current crop of Labour MPs, 20 would not have been in the Commons under the system which is being put to the public in Thursday's referendum; eight of those 20 have signed up to the No to AV campaign. Among them is Ian Austin, Gordon Brown's former parliamentary private secretary, who clung on by just 649 votes last year in Dudley North. The researchers at Essex University have calculated that the second-preference votes of Ukip and BNP supporters would have handed it to the Tories.

Emily Thornberry, the Labour MP for Islington South and Finsbury, would have seen her seat fall to her bitter Liberal Democrat local rivals. Jim Dowd, the long-standing MP for Lewisham West and Penge, would also have been ousted by the Liberal Democrats. Other No to AV Labour supporters who would have lost out are:

* Toby Perkins, who beat the Liberal Democrats in Chesterfield by 549 votes.

* Simon Danczuk, who managed to capture Rochdale from the Liberal Democrats despite Gillian Duffy's infamous monstering of Gordon Brown when the prime minister visited the town during the election campaign.

* Ian Murray, who picked up Edinburgh South with less than 35 per cent support, and a majority of just 316.

* Diana Johnson, a former minister, who just managed to beat a Liberal Democrat challenge in Hull North by 641 votes.

* Geraint Davies, whose return to Parliament as MP for Swansea West succeeded by only 504 votes.

For the Tories, in addition to Mr Eustice, 20 current Tory MPs – all of whom favour first past the post – would have lost under AV in 2010. Guto Bebb (Aberconwy), Mary Macleod (Brentford and Isleworth), Anna Soubry (Broxtowe), Matthew Offord (Hendon), Mike Weatherley (Hove), Eric Ollerenshaw (Lancaster & Fleetwood), Mark Spencer (Sherwood) and James Wharton (Stockton South) would have lost their seats to Labour.

Charlotte Leslie (Bristol North West), Jason McCartney (Colne Valley), Andrew Jones (Harrogate & Knaresborough), Glyn Davies (Montgomeryshire), Anne Marie Morris (Newton Abbot), Nicola Blackwood (Oxford West and Abingdon), Rob Wilson (Reading East), Anne Main (St Albans), Sarah Newton (Truro & Falmouth), Richard Harrington (Watford), John Penrose (Weston-super-Mare) and Julian Sturdy (York Outer) would have lost their seats to the Liberal Democrats.

Two other Tories who would have lost their seats have a more ambiguous attitude to reform. Jonathan Evans, the MP for Cardiff North, has previously backed electoral reform but has not intervened in the AV debate. And David Mowat, the MP for Warrington South, said he is "agnostic" on the issue.

Survival instinct kicks in

The 29 'No to AV' MPs who, based on research by Essex University and The Independent, most likely would not have won their seats at the 2010 general election had AV been in operation