EU referendum: Major warns against 'flirting' with EU exit
Sir John Major has warned David Cameron against "flirting" with leaving the EU "at a moment when the whole world is coming together".
The former prime minister said Thursday's EU reform talks should not be regarded as "High Noon".
And they "should not decide whether or not we remain inside the European Union", he told BBC Radio 4's Today.
In Parliament, Mr Cameron said he had a "great record on Europe" and would get "the best deal" for the British people.
Speaking during Prime Minister's Questions, Mr Cameron - who has refused to rule out campaigning for an exit if the EU does not agree to his reform demands - said he had won concessions before from the EU and his approach to the referendum was to "get a good deal and trust the British people".
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Sir John, whose seven years in Number 10 were dominated by internal Conservative Party rows over Britain's future in Europe, said he was not a "starry-eyed European" and he could understand "frustrations" with the EU, which were "entirely justified".
He also said he could not "get inside" David Cameron's mind - and was anxious not to become a "backseat driver" to the prime minister.
But he said "flirting with leaving at a time when the whole world is coming together is very dangerous and against our national interests".
He said the UK should not "break off" and head into "splendid isolation".
Analysis, by BBC Deputy Political Editor James Landale
Sir John Major rations his public utterances. So when the former prime minister gives an interview, he tends to have something to say and people tend to listen. And his remarks on the Today programme were clearly directed at David Cameron.
Sir John was effectively warning the prime minister not to base his campaign for Britain to stay in the EU entirely on the reformed relationship he is hoping to negotiate this week.
"This renegotiation is important," he said, "but it shouldn't decide whether or not we remain inside the European Union." Instead, Sir John implied that Downing Street should be doing more to make the broader case for staying in.
He said that "flirting with leaving is dangerous", heading off into "splendid isolation wouldn't be in our interests", there would be "acrimonious negotiations with an irate ex-partner", it would not save much money, nor better control our borders but it would lead to a "fractured" UK because of the "high probability" of Scotland voting for independence.
So Sir John's implicit message to Mr Cameron - as he prepares for some tough negotiations in Brussels - is that he must start making the wider case for EU membership if he wants to win the forthcoming referendum.
He said there would be a "high probability" Scotland would have another independence referendum and the UK's international standing would also suffer.
The UK would not be better able to control immigration, nor would it make the UK Parliament more sovereign because to trade with the EU "we would have to accept its regulations," added Sir John.
"If we leave the EU it won't be a friendly departure, it will be very acrimonious," he told BBC Radio 4's Today programme.
He said he could understand why Mr Cameron had decided to hold a referendum on remaining in the EU to end the "long-running and tiresome" row about the issue - but he predicted that the British people vote to stay in.
Mr Cameron will join other EU leaders in Brussels on Thursday for substantial talks on the UK's demands for reform.
A deal could pave the way for the government to announce when it will hold an in/out referendum on Britain's membership, which Mr Cameron has promised will be held by 2018.
Leave.EU - one of the groups campaigning for Britain to exit the bloc - said Mr Cameron should "stay and home and put his feet up" because "he isn't asking for anything that people actually want".
"His grandstanding around ending migrants accessing benefits will do nothing to reduce the number of people wanting to come here," said Brian Monteith, the group's head of press.
European Commission President Donald Tusk has said Thursday's talks should "pave the way" for an agreement by the next gathering of EU leaders in February.
Mr Tusk said the discussions should focus on the "most controversial" elements of Mr Cameron's reform demands, which are likely to centre on his calls for a four-year wait before EU migrants can receive working-age benefits.
"The stakes are so high that we cannot escape a serious debate with no taboos," Mr Tusk said.
Mr Cameron is reported to have warned in private that he will lead the EU exit campaign if he does not get what he wants from other EU leaders. His public comments have been more measured, with the PM repeatedly saying he "rules nothing out".
Speaking at PMQs, he said: "What I will be doing is getting the best deal for Britain, that is what we should be doing. This government was the first to cut the EU Budget, it was the first to veto a treaty, the first to bring back substantial powers to Britain."
Also speaking on Wednesday, UKIP leader Nigel Farage described the renegotiation as a "charade" which would result in only "minor and inconsequential" changes, and said those campaigning for the UK to leave the EU had "momentum on their side".