The elections watchdog has said that a referendum on the euro should not be held in parallel with any other local, assembly or parliamentary elections.

The Electoral Commission warned that any such move could confuse the electorate.

The move puts significant pressure on the government not to hold a vote on one of its preferred dates, May 1 next year, although it retains the power to reject the commission's advice.

The elections and referendums watchdog said that while there might be a beneficial effect on turnout from combining the votes, it could confuse campaigning and restrict full debate on all the issues.

"As there may be cross-party campaigning on a fundamental referendum of this sort, this could cause significant confusion amongst the electorate if combined with normal party election campaigning," said the commission.

It warned that a euro vote would influence other polls "to an extent that may compromise the electorate's will" in the other elections.

It added that there would be considerable problems controlling the administration of simultaneous polls, in areas such as campaign expenditure.

"Referendums on fundamental issues of national importance should be considered in isolation," said a statement.

"The Electoral Commission is therefore of the view that a referendum on the single European currency should not be held at the same time as the parliamentary and local government elections in Scotland, and the assembly elections in Wales and Northern Ireland due in May 2003."