Theresa May risks a showdown with MPs after it emerged some prisoners are to be given the right to vote.

Plans drawn up by Justice Secretary David Lidington will allow prisoners who are eligible for day release to vote if they are on the electoral role.

It means only a minority of prisoners will be allowed to take part in elections, but the measure is likely to encounter opposition from Conservative MPs. Former prime minister David Cameron once said the thought of prisoners voting made him feel "physically ill".

And Black Country Labour MP John Spellar (Lab) said: "This must not be the thin end of the wedge."

He added: "It seems this will only involve a small number of prisoners but Ministry of Justice has not made it clear how many.

"This is a shambolic way of announcing a policy."

It follows a 12-year dispute with the European Court of Human Rights, which ruled in 2005 that stopping prisoners voting was a breach of their human rights.

The Sunday Times newspaper reported that Conservative MP Peter Bone had already criticised the plan. He told the newspaper: "I’m not in favour of letting prisoners vote. I find it extraordinary. It’s a bonkers decision. I think a lot of MPs will be concerned about this."

And Philip Davies, the Conservative MP for Shipley, said: "I am wholly opposed to it. I am against giving prisoners the vote. Prisoners released on temporary licence are still prisoners."

Only prisoners in jail for a year or less are likely to be able to vote, because people fall off the electoral roll after 12 months and it's not possible to rejoin it while in prison.

A Government spokeswoman said: “We do not comment on speculation. Our policy on prisoner voting is well established – it remains a matter for the UK to determine, and offenders in prison cannot vote.”