Q:

Is an in/out referendum a certainty?

A: No. David Cameron plans to contest the next election on a campaign of renegotiating the terms of British membership of the EU and then putting the resulting deal to the electorate in an in/out referendum by the end of 2017. So the Tories have to win the next election to ensure a vote.

Q: Isn't Cameron pro-Europe?

A: Yes. He previously said he would campaign to keep Britain in a renegotiated EU. However, his line has recently hardened and he has said he could be forced to recommend a No vote if he fails to get the UK an opt-out from Brussels' "ever-closer union".

Q: So what exactly do the Tories want to renegotiate before they would back a Yes?

A: Among other aims, the Conservatives, with UKIP breathing down their necks, want to restrict freedoms of movement and labour within the EU, despite more than 2.3m British citizens living elsewhere in the bloc.

Q: Are their demands practical?

A: Not according to Jose Barroso, the outgoing president of the European Commission, who has said Tory proposed immigration caps would be "unacceptable" .

Q: Is a vote to leave likely?

A: Polls vary. Some have shown a UK majority for quitting before renegotiation. However, recent polls have shown a steady majority in favour of staying if some kind of new settlement can be reached.

Q: Are Scottish attitudes to Europe different to those in rest of UK?

A: Yes. Research shows just four of Scotland's 51 Westminster seats would deliver a Yes, compared with most in England.

Q: Didn't we vote on this before?

A: Yes. The UK joined the Common Market in 1973 and two years later voters decided by two to one to stay in. Support in Scotland was lower than England or Wales at 58% per cent for staying, compared with 68% in England. The Western Isles and Shetland were the only places in the UK to call for an exit.