David Cameron has hinted that a Conservative government could hold an early referendum on Britain’s membership of the European Union after getting “proper, full-on treaty change”.

The prime minister has promised he would hold an in/out referendum before the end of 2017 if he were still in power, but he said on Sunday that he would be “delighted” to bring that forward.

He told the BBC1’s Andrew Marr Show: “The referendum must take place before the end of 2017. If we could do that earlier, I would be delighted. The sooner I can deliver on this commitment of a renegotiation and a referendum – the sooner I can deliver on that the better.”

Cameron also signalled he would expect cabinet ministers to keep to the government position on Britain’s membership, rather than allowing them to follow their consciences with a free vote. This is likely to cause some discord if Cameron were to lead the next government, as several senior Tories have been making it clear they would want to campaign for the UK to leave.

“There are Conservative members of parliament who want to leave the European Union come what may. But if you’re part of the government then clearly you’re part of the team that is aiming for the renegotiation referendum,” he said.

Before holding a poll, Cameron has pledged to renegotiate the terms of the UK membership with other member states. This would probably have to take place earlier rather than later because France and Germany are likely to be preoccupied by elections in 2017.

Cameron is holding talks with Angela Merkel when the German chancellor visits London this week and is likely to raise the prospect of reducing EU immigration by clamping down on benefits for migrants. At one point, Downing Street floated the idea of a cap on EU migrants but this has been squashed by Germany.

Asked about proposed changes, he said: “They do involve … proper, full-on treaty change. We need to get out of ever-closer union. That is something that shouldn’t apply to the United Kingdom. We need parliaments to be able to combine to block regulations. I think that is very important. We need guarantees that as the single currency gets more countries in it, the single market which Britain remains in is properly protected. Crucially, on the question of immigration we need these very big changes that I’m putting forward to the welfare system that will require treaty change.”

He added: “I think that everyone can understand that under the proposals I have that if someone comes to Britain from Europe looking for a job they don’t get unemployment benefit; if they don’t have a job within six months they have to go home; they have to work for four years before they can claim things like tax credits. Crucially you don’t get child benefit with respect to children that you leave at home with your family in other countries. Those four changes are hugely important.”

Pat McFadden, Labour’s shadow minister for Europe, said it was extraordinary that Cameron would not say how he planned to vote in his own referendum.