Gordon Brown has been urged by returning officers not to hold a November election because errors on the electoral register mean that up to a million people may be unable to vote.

An autumn election could be “the worst in living memory”, according to John Turner, the chief executive of the Association of Electoral Administrators, who said that “nobody sitting in my situation could guarantee that [an autumn poll] will be less than trouble-free.”

He said that there would be problems with postal voting, where the lessons from May’s elections have not yet been put into effect.

He also voiced concern that new constituency boundaries and electoral software could create “a real logistical nightmare”.

Mr Turner is worried about the accuracy of the electoral register. He said that the new register, which is being updated at the moment, does not come into effect until December 1.

A November election would be held using the 2006 electoral register, which means that people who have changed their details recently and want to vote must put their details on the “rolling register” up to 11 working days before polling. Many people may not have notified their local town hall of any changes.

Asked what he would say to the Prime Minister about calling a snap poll, Mr Turner replied: “Keep your hand away from the phone.” He added: “It’s not whether I want it, it’s whether he wants it, of course. But the question is that, with the best will in the world, nobody sitting in my place could guarantee that it will be trouble-free. The real problem is that we could run into uncharted water in terms of these problems.”

Mr Turner told The Politics Show on BBC One that recent changes in the law designed to tackle identity fraud meant that all postal ballots had to have special “identifiers” for computer checks. That had caused serious difficulties during the local elections, and the problems would be “multiplied several times over” in a general election because turnout would be higher.

The law has also yet to be changed for Scotland, which raises the prospect of operating different counting systems in different parts of the country, he added. “We would have a dual system running. Those people in Scotland not doing it, those people in England and Wales having to do it.”

Eric Pickles, the Shadow Minister for Communities and Local Government, said: “Many people who have completed the electoral registration form believe that they are now registered to vote. They are not.”

Mark Lancaster, Tory MP for Milton Keynes North East, said that he and his colleagues had picked up that an early election could cause a logistical nightmare.

“It’s pretty clear that returning officers appear to be dreading an early election because all the registers seem to be in complete flux. In order to get the work done on time, there would be a significant cost implication.”

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