One in three voters could still change their minds about how to vote at the General Election – which will be the closest in decades.

A survey for the Sunday Mirror found that 36% might change their minds before polling day on May 7, including 51% of those voting Lib Dem in 2010.

Just over half (53%) know for sure who they will back.

Our poll shows Labour has clung to the one-point lead it had over the Tories last month.

Ed Miliband’s party is still on 34% with the Tories on 33%.

UKIP remain on 18% and in third place.

Nick Clegg’s Lib Dems are down one point on a lowly 7% while the Greens are up one on 3%. Other parties total 5%.

ComRes head of political polling Tom Mludzinski said: “With a third of people still making up their minds, the result of this election really is up in the air. A number of outcomes are still possible and every vote may have a huge impact.”

A total of 39% of the people polled said they were already bored with news about the election.

Roughly the same proportion – 41% – think the Tories would break up the NHS if they win as believe Labour would bring economic chaos (42%).

Worryingly for Labour in the wake of claims Mr Miliband wants to “weaponise” the NHS, half of voters (49%) think he is using the issue for political ­advantage. The total includes almost one in five Labour voters (19%).

Mr Miliband praised the Mirror’s NoVoteNoVoice campaign, which aims to persuade a million new voters to go to vote.mirror.co.uk to register.

Labour figures show almost a million people have disappeared from the Electoral Register.