Tony Blair: Quitting EU would be 'huge problem' for UK
It would be a "huge problem" for the UK if people vote to leave the European Union, former Prime Minister Tony Blair has warned.
David Cameron has promised an in/out referendum before the end of 2017 if the Tories win the next election.
He says the UK's relationship with the EU needs to change.
But Mr Blair said a decision to quit would reduce the UK's "weight" in the world and there would be "uncertainty" in the lead-up to the vote.
In a speech last month, Mr Cameron promised an in/out referendum before 2018, following a renegotiation at government level.
This came amid growing concern among many Conservatives over developments within the EU, particularly over the effects of increasing financial and political integration by eurozone member states.
'Weight and influence'
But Mr Blair, who was Labour prime minister from 1997 to 2007, told BBC One's Andrew Marr Show: "We are in an uncertain situation. They [people in Europe] ask me if Britain's going to get out of Europe. I can't answer that question conclusively now."
Mr Cameron's pledge was not "sensible", he said, adding: "We are in a situation where, four or five years down the line, there's uncertainty.
"If Britain did want to get out of Europe, it would be a huge problem for our country."
Mr Blair also said: "If we want to exercise weight and influence and power in the world, why would we want to separate ourselves from the biggest political union and economic market on our doorstep?"
But Mr Cameron's supporters argue the EU is out-of-touch, too expensive and unsupportive of the UK's national interest and that a looser, more purely economic, relationship would be better for both sides.
Foreign Secretary William Hague told BBC One's Sunday Politics the Conservative leadership had "done what we set out to do", adding: "We want a new settlement. We intend to get that."
He said a future Conservative government would use its "judgement" on whether to back leaving or staying in the EU, after the government-level renegotiations had ended.
Asked whether setting the date for a referendum in advance was likely to create uncertainty, the foreign secretary replied it was a "realistic timetable", given the time it would take for the situation following the changes in the eurozone to become clear.
In his interview, Mr Blair also spoke about the fight against al-Qaeda saying it would take "a generation" and be "like the fight the West had over a long period of time with revolutionary communism".
He added that the UK was right to the support French intervention in Mali by offering training to African troops.
Mr Blair also said he talked to Mr Cameron and Labour leader Ed Miliband "from time to time".
"When you've been there, you know about the difficulties of the job," he said.
Mr Blair added that "the last thing I would want to do with either individual is be one of those pains in the neck saying 'I would've done this or that.'"