If Prime Minister David Cameron allows his cabinet ministers a free vote in the European Union referendum division will ensue that could spark a "civil war" in the Conservative party, Lord Michael Heseltine has warned.
Speaking to BBC Radio 4's Today programme, Heseltine said that if Cameron did choose to let ministers vote with their consciences he would be made a global "laughing stock".
"There is a collective loyalty and the consequence of having a free vote, if you like, would be that the divisions, the divisiveness, the bitterness that would flow would actually, in my view, make the Prime Minister's position very difficult," the former minister added. "If they feel so strongly then they should resign, although it is quite difficult for me to understand how they're in the cabinet in the first place."
However many have called on the Prime Minister to do the opposite of what Heseltine wants, urging him not to whip ministers, including Foreign Affairs Select Committee chairman Cripsin Blunt, former environment secretary Owen Paterson and former defence secretary Liam Fox.
Cameron has promised to hold an In/Out referendum on the United Kingdom's membership of the EU before the end of 2017, after he has wrapped up the lengthy and ongoing negotiations.
On Friday Cameron said the UK's relationship with the EU will "fundamentally change" in 2016, following talks with his counterparts in Brussels.
The Prime Minister is hoping to secure a deal at a meeting of EU leaders in February, after which the referendum will follow, coming as soon as the summer of 2016.
However, he is under pressure as other European leaders have indicated they may be unwilling to accommodate one of Cameron's key demands of restricting in-work benefits for EU migrants for the first four years they are in the UK.
While Cameron has not ruled out campaigning for Brexit if he does not secure the treaty changes he is aiming for, it is anticipated he will recommend Britain remaining in the EU.