A plan to overhaul the way that Britain votes during general elections looks set to be shelved, according to a confidential government document obtained by The Times.

Moves to reengage voters by introducing proportional representation for Westminster elections have been dismissed by officials, who fear that it could lead to political instability and confusion.

Changing the voting system would increase the likelihood of minority governments and coalitions, which can be a “drag on effective government”, officials investigating voting systems found.

It is uncertain whether the move would increase turnout or ensure that MPs more closely reflected the ethnic or gender make-up of Britain, the report says. It highlights the problems that were created by the Blair Government’s innovations to the voting system for nonWestminster elections, such as the high levels of rejected votes resulting from complex ballot papers. It reveals the “friction” in the Scottish Parliament and Welsh Assembly between Members who were selected to represent constituencies and those from lists drawn up by party managers.

The Review of Voting Systems in the United Kingdom was completed in draft form last November but will not be released to the public until December. The Conservatives said last night that they feared that Gordon Brown would attempt to water down the tough language that cautioned against proportional representation to smooth relations with the Liberal Democrats in the event of a hung Parliament.

The draft report, marked “restricted”, questions the viability of the only option that Mr Brown is thought to have considered as a serious alternative to the present system. It says that the Alternative Vote system – where voters rank candidates in order of preference – is “capable of producing even more disproportionate outcomes nationally than first past the post”.

Although the report does not oppose the introduction of a more proportional voting system, it uses tough language to dismiss many of the arguments in favour of PR and could easily be used by Mr Brown if he decides to rule out such a change. It says: “One of the main arguments advanced in favour of some form of PR is that it will make everyone’s vote count in some way, and therefore give more people an incentive to vote. The cause and effect is not proven.”

The report highlights the example of New Zealand, which abandoned first-past-the-post voting in 1996, bringing an end to a series of majority governments and coalitions amid falling turnout.

The 110-page report also found: The current voting system favours Labour, particularly when it is the party of government. Most of the alternatives to first past the post are not “genuinely proportional”. Only in Northern Ireland, where the Single Transferable Vote is used, has the system achieved something close to genuine proportionality. Proportional systems do not increase turnout. In all elections in the UK that have used proportional systems, turnout has been considerably lower than in general elections. Existing proportional schemes have done relatively little to increase ethnic minority representation.

The report concluded: “Overall, it is difficult to draw a clear causal relationship between a particular voting system and particular outcomes, be they turnout, connectedness to the citizen, social representativeness or any other criteria explored in this review.

“Coalition or minority government is prevalent where proportional systems are used and this can be viewed as either representing a greater diversity of input to policy-making, or a drag on effective government.”

The report calculates that had the last election been run under a more proportional system, the main beneficiary would have been the Liberal Democrats and the biggest loser Labour. The Conservatives would be affected only marginally by most systems.

The Ministry of Justice, which replaced the Department for Constitutional Affairs, which oversaw the report, refused to comment because the report was “work in progress”.

Nick Herbert, the Conservative constitutional affairs spokesman, said: “This leaked copy of the review blows out of the water the case for changing Britain’s tried and tested electoral system. The Government’s own report admits that proportional representation has caused voter confusion and not increased turnout. And it says that Alternative Vote would produce even more disproportionate results than any other system. I fear the real reason for the delay in publishing this review is Labour trying to fiddle the dossier. This Government has repeatedly meddled with the electoral system for partisan advantage, undermining public confidence in the integrity of the ballot.”

Voting systems

First past the post (FPTP) Used in: General elections How it works: Put an “X” next to the candidate you support. The one with the most votes wins

Supplementary Vote London Mayoral Ballot paper has two columns. Voters mark an “X” in the first column for their first choice and another in the second column. If no candidate gets 50 per cent the two highest scoring candidates are retained; the rest are eliminated and their votes reallocated

Alternative Vote (AV) Not used in UK Each voter ranks candidates in order of preference. If no candidate gets more than 50 per cent the one with the least votes is eliminated and his votes allocated according to second choices until someone gets 50 per cent

Single Transferable Vote (STV) Northern Ireland Assembly Each constituency elects between three and five MPs depending on size. Voters rank the candidates 1, 2, 3 etc. The candidates with the least votes are eliminated and their votes redistributed. This is repeated until there are only the required number of candidates left

Additional Member System Scottish Parliament, Welsh Assembly, London Assembly Each voter has two votes: one for a single MP via FPTP and one for a regional or national party list. In Scotland, 73 of the 129 seats are allocated according to constituencies; the rest are chosen proportionately using party lists

Alternative Vote Plus Proposed by Jenkins commission Voters would have two votes - one for a constituency MP and the other from a regional list. The constituency MPs are elected by AV (see above). The “top-up” MPs are elected using lists prepared by party managers

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