Conservative MPs have been warned they could shoot themselves in the foot if they try to end the right of students to vote in the constituency where they study.

The expansion of ÖйúAƬ has raised fears among Conservatives in marginal seats that larger concentrations of students could mean they will become the victims of tactical voting at the next General Election.

Some are reported to be pressing for a Bill to stop students from being automatically included on the electoral roll in the constituency of the place where they are studying.

The right of students to be included on two electoral registers has been tested in court, and most living in halls of residence are now automatically placed on the electoral roll by their institutions. This informal arrangement is overseen by the equal opportunities and general department of the Home Office, whose rag-bag of responsibilities also include gaming and new religious movements and cults.

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Tory backbenchers are hoping that if that arrangement were to end, and students became responsible for registering themselves with the local returning officer, large numbers would not do so and revert to voting in their home constituency.

Their fears about tactical voting are partly a carry-over from the last General Election when the National Union of Students launched a campaign called Target 70, in which it encouraged students to target marginal seats to lobby MPs over student issues. The NUS was accused of conspiring with Labour to pick out Tory marginals, and it was estimated that the Conservatives lost up to three constituencies because of this.

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Political and electoral law experts say the MPs' worries are probably well-founded. Not only are there more students than at the last election, but a higher proportion will probably register to vote because they will not be trying to avoid paying the poll tax.

Robert Waller, author of The Almanac of British Politics, named John Patten's seat of Oxford West and Abingdon as one possible target for tactical voting by students. The former education secretary's majority of just under 4,000 could be demolished if the large student population decided to hold his outspoken views on student union accountability against him. Other vulnerable seats include Loughborough, whose former MP, Stephen Dorrell, the Secretary of State for Health, used the recent boundary changes to escape to a "safe" seat; Stirling, where Scottish Secretary Michael Forsyth's majority is wafer thin; and other marginals with major institutions nearby such as Portsmouth South, Luton South and Exeter.

But Dr Waller suggested the Tories could end up making their position even more vulnerable through electoral reforms which were likely to prompt tactical voting campaigns and would affect Conservative students as much as Labour.

"Labour and the Liberal Democrats tend to be much better than the Conservatives at organising tactical voting. The effect of the proposed changes could therefore be the opposite of that hoped for by the Tories," he said.

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Iain MacLean, fellow in politics at Nuffield College, Oxford, suggested the proposed changes would be impractical and seen as too partisan to gain support anyway.

"There are many changes that need to be made in electoral law which are of much greater democratic importance than this," he said.