Germany had a secret veto over what David Cameron could demand as part of his renegotiation of Britain’s membership of the EU, a former Cabinet Minister claimed today.

Iain Duncan Smith, who resigned as Work and Pensions Secretary in March, alleged that a key speech by the Prime Minister in which he was due to demand restrictions on all EU migrants coming into the UK was partially dropped at the insistence of Germany.

And he even claimed there was an empty chair in Downing Street – dubbed the German chair – that symbolised their power in dictating the terms of any deal David Cameron would be able to negotiate.

Delivering his harshest attack on Mr Cameron yet in the EU referendum fight Mr Duncan Smith told the Sun newspaper: “It’s like they were sitting in a room, even when they were not there.

“There was a spare chair for them - called the German Chair.

“They have had a de facto veto over everything.”

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He said one of the most obvious episodes was just before Mr Cameron delivered a key speech to set out what he would demand from the EU as his price for backing a stay vote in November 2014.

“I saw the draft,” he said. “I know that right up until the midnight hour, there was a strong line in there about restricting the flow of migrants from the European Union – an emergency break on overall migration.

“That was dropped, literally the night before.

“And it was dropped because the Germans said if that is in the speech, we will have to attack it.

“The whole thing was shown to them.

“The Germans said from the outset, you are not getting border control. Full stop.”

Mr Duncan Smith said Downing Street saw Berlin’s support as crucial to win a package from the other EU leaders that the PM could sell to the British people.

But that gave Germany huge power over it, he insisted.

“There is no question in my mind that keeping the Germans on side was the only thing that really mattered,” he said.

“We wanted to use the Germans to work the others in the room. They had the ultimate power over it.”

But the former Cabinet minister claimed the PM’s Berlin strategy meant he was dictated to by a foreign power to suit its own interests rather than Britain’s.

“We put ourselves in a compliant position to another country which doesn’t have your best interests necessarily at heart."

Mr Duncan Smith is due to make a speech later today outlining why he believes Britain should leave the EU.

A Number 10 source said: “The Prime Minister made clear at the time that the government had looked at an emergency brake but he decided it was not the most effective way forward.