The Conservatives have always been divided over Europe - and a three line whip from their party to vote down a chance to hold a public referendum on Europe has led to threats of a "mutiny". Tory sources have predicted that ministerial aides will resign over the issue, telling Huff Post UK that "people may well be surprised" by who goes.
The eurosceptics go beyond the usual suspects, such as influential backbencher Mark Pritchard who this morning said the issue was about "country first, party second and career last." A number of government special advisers have been associated with think-tanks and campaigns against the UK's membership of the EU - and two current ministers, Alan Duncan and David Willetts, also rebelled against John Major's government over the Maastricht Treaty.
While some in the prime minister's office, such as Ed Llewellyn, are though to be pro-Europe, his advisers Steve Hilton and Gabby Bertin are thought to be skeptical. Last week it was revealed Bertin had worked for the right-wing group Atlantic Bridge, and Hilton has called for the UK to pull out of Europe.
Iain Duncan Smith's special adviser formerly worked for the Taxpayers' Alliance, who have mounted strong campaigns against EU waste.
Paul Stephenson, a newly appointed department of health special adviser was head of research at Open Europe, a think-tank which calls for "radical reform" of the EU.