Northern Ireland secretary Owen Paterson has said a referendum on the UK's membership of the European Union is "inevitable" if eurozone countries form a tighter union.
Speaking to the Spectator magazine, the eurosceptic cabinet minister said Britain was at risk of being permanently outvoted by a united eurozone bloc within the EU.
“If there was a major fundamental change in our relationship, emerging from the creation of a new bloc which would be effectively a new country from which we were excluded, then I think inevitably there would be huge pressure for a referendum,” he said.
“I think there will have to be one [a referendum], yes, because I think the pressure would build up.”
He added: “This isn’t going to happen immediately because these negotiations are going to take some months. But I think down the road that is inevitable.”
Paterson's comments emerged as David Cameron faced a barrage of questions in the Commons from his own MPs about Britain's relationship with the EU at prime minister's questions on Wednesday.
The prime minister pledged to safeguard British interests. "The more that countries in the eurozone ask for, the more we will ask for in return," he said.
Paterson's intervention will add to the pressure on comes after work and pensions secretary Iain Duncan Smith said a referendum should take place in the event of any “major treaty change”.