The planned referendum on the UK's membership of the European Union should be changed because some voters are unaware Britain is already a member, the elections watchdog has said.

MPs are currently considering proposals to go to voters in 2017 asking: "Do you think that the United Kingdom should be a member of the European Union?"

But the Electoral Commission said a more neutral alternative would be "Should the United Kingdom remain a member of the European Union or leave the European Union?".

Any change in the wording is likely to delay the passage of Tory MP James Wharton's private member's bill, which is already likely to have a rocky ride through parliament.

He warned earlier this year that any amendment would make the progress of the bill more difficult because opponents would be able to seize on parliamentary techniques to help bring it to a halt.

Wharton tweeted that he had received the commission's recommendation "but initial reaction is no need to change qu[estion], recommendation not strong but will reflect".

Earlier this year MPs voted unanimously for Britain to be given an in-or-out referendum on its membership of the EU by 2017 after Labour and Liberal Democrat MPs abstained.

The bill returns to parliament on 8 November.

Jenny Watson, who chairs the commission, said: "Any referendum question must be as clear as possible so that voters understand the important choice they are being asked to make. This is why we have rigorously tested the proposed question and have taken voters' responses and understanding into account in developing alternatives.

"We found that a few people did not understand whether or not the UK was a member of the EU. Providing enough information to make this clear to people creates a risk of a perception of bias for any question which offers yes and no options.

"That's why we're presenting two possible questions to parliament: one that keeps with the recent tradition of yes-no referendum questions and an alternative in a different format which was perceived by voters to be more neutral.

"Parliament will now need to discuss our advice and decide which approach the bill should take."