Education Secretary Michael Gove's parliamentary aide has said he would vote for a Commons amendment backing an EU referendum.
Conservative MP Gavin Barwell told BBC Radio 4's Today programme, "I completely support the policy that was set out by the Prime Minister in January but what we need to do is to convince a sceptical electorate that we actually mean it".
"The electorate at the moment doesn't have a great deal of trust in politicians in general and many people feel they have been promised referenda in the past and they haven't happened", he continued.
"So this isn't an issue about Conservative MPs trusting David Cameron. It's about using the legislative process to convince the electorate that the clear commitment he gave in his speech is going to happen".
Cameron has pledged to back a Conservative MP's EU referendum bill, as Cable labelled the move potentially 'damaging' for the country.
114 Conservative backbenchers have voted in favour of a eurosceptic motion to amend the Queen's Speech in defiance of the Prime Minister.
David Cameron has denied he has buckled under pressure from his backbench MPs over the EU debate.