If the missing electors had voted, at least six more seats would have been won by Labour and two by the Liberal Democrats, the study claims. The Tories' majority in the House of Commons would have been reduced by 16, from 21 to five, leaving them vulnerable to losing it in by-election defeats.
The report, by Iain McLean, professor of politics, and Dr Jeremy Smith, a lecturer in economics, both of the University of Warwick, is the first public attempt to put a figure on the number of voters driven off the electoral roll by the poll tax.
The authors analysed the 1991 census figures, published by the Office of Population Censuses and Surveys, which show that one million people were missed by the census. The census count was originally almost two million lower than the latest OPCS population estimate of 50.95 million. A follow-up survey accounted for one million, leaving another million still 'under enumerated'.
The working paper, called The UK Poll Tax and the Declining Electoral Roll: Unintended Consequences? states: 'In total the poll tax, it is estimated, can account for slightly more than one third of the estimated one million shortfall. The total estimated shortfall of the electorate due to the influence of the poll tax is 352,625, although this is markedly short of the reported one million underestimation calculated by Population Trends (published by the OPCS).'
The authors say that the figure of eight seats which the Tories would otherwise have lost is a 'conservative' estimate. The five English seats are Bristol North West, Hayes and Harlington, Edmonton, Bolton North East, Portsmouth South. The authors did calculations using data from the 364 English local authorities, but the report states: 'By analogy with the English cases it seems safe to add Ayr, Vale of Glamorgan and Brecon and Radnor to the list of seats which the Conservatives would not have held.'
Labour would have won four of the seats in England, Ayr and Vale of Glamorgan and the Liberal Democrats would have won Portsmouth South and Brecon and Radnor.
The report concludes: '1992 is not the end of the story. It is unlikely that those who have come off the electoral register will willingly flock back on; the 1991 electorates must by law determine parliamentary boundaries from 1996 to probably 2011.'
The OPCS acknowledged on Friday that 572,000 people both failed to return the census form and 'eluded' follow-up interviewers - 220,000 were men aged between 20 and 29.
Commenting on Prof McLean's report, Jack Straw, Labour's environment spokesman, said: 'All of us who worked in the election are absolutely clear that a lot of potential Labour voters, particularly younger voters, where we had an ostensible lead, had not registered.
'Many of us thought the Tories had a hidden agenda with the poll tax, to deprive a lot of young people of their vote, particularly those already deprived of their jobs or training.'
The Department of the Environment refused to comment but said that the OPCS had no hard evidence that the poll tax led to census evasion.Reuse content