Legislation paving the way for a referendum on whether the UK should stay in the EU is to be debated by MPs for the first time.
The EU Referendum Bill is expected to pass comfortably at second reading, its first legislative hurdle in Parliament.
It comes amid Conservative tensions over whether ministers could lose their jobs if they campaign to exit the EU.
David Cameron has denied saying they would have to back him or go, claiming comments of his were “misinterpreted”.
The prime minister was forced to clarify his position on Monday after a number of former ministers expressed concerns that colleagues would have to leave the government if they wanted to make the case for leaving the EU during a forthcoming referendum.
London Mayor and Conservative MP Boris Johnson told LBC radio on Tuesday that ministers should be given free rein to campaign as they want ahead of the vote.
He said it would be “safer and more harmonious” that way, questioning the need to “bind everyone in”.
‘Vote by 2017’
Mr Cameron’s plan is to renegotiate the UK’s relationship with the EU ahead of an in/out vote by the end of 2017.
He says he is confident of securing the changes he wants so he can push for a Yes vote to stay in Europe, but says he “rules nothing out” if his demands to EU leaders on issues such as immigration, welfare, national sovereignty and further integration are rejected.
The legislation required to authorise the referendum will be debated for the first time in the Commons on Tuesday, when MPs will debate the general principles of the EU Referendum Bill.
The bill states that a referendum will take place by the end of 2017, with voters being asked “Should the UK remain a member of the European Union?”.