David Cameron has mocked Labour's "feeble" position on whether or not to support an in/out referendum on the UK's membership of the European Union.
On Friday MPs will vote on a backbench Bill, piloted by Tory MP James Wharton, that would commit the government to holding a referendum by 2017.
David Cameron has instructed Conservative MPs to vote in favour of the legislation which, while notionally a private member's bill, was initially cooked up in Downing Street.
The prime minister was unable to introduce a government bill along the same lines as Nick Clegg and the Lib Dems oppose holding a public vote.
However Ed Miliband has instructed his MPs to abstain on Friday - which means the Bill is likely to clear its first hurdle and make its way to committee stage where it will undergo detailed examination.
Speaking in the Commons today, Cameron seized on Miliband's decision as proof of a internal-shadow cabinet split over what to do.
"When it comes to this issue of a referendum, you can either be in favour of holding an in/out referendum or you can be against holding an in/out referendum - surely you must have an opinion," he said. "What is the party opposite going to do?"
Noting Labour's decision to abstain, he added: "The whole of the country will find that completely feeble."
Addressing Miliband, Cameron said: "He has said he is not in favour of a referendum, the shadow chancellor has said it's pretty stupid not to have a referendum and his chief advisor has said its conceivable they might have a referendum."
The prime minister was referring to Lord Wood, one of Miliband's top advisers who told The Huffington Post UK last week Labour may decide to promise a referendum close to the 2015 general election.
Miliband also took time to make fun of Cameron's macho approach to meeting other European leaders last week. On Friday the prime minister said he had traveled to Brussels prepared for an "ambush" and to "lock and load and have one up the spout".
The Labour leader said the rhetoric "sounded more 'Carry on Up The Council' than High Noon'."