It would be a "huge problem" for the UK if people vote to leave the European Union, former Prime Minister Tony Blair has warned, according to BBC News.

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 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, 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.

But Blair, who was Labor 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."

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."

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 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.