The foreign secretary has warned Britain's pro-Europeans that they must "work harder and speak louder" to promote the benefits of the European Union.

In a speech to the Chester Chamber of Commerce, Jack Straw called for a greater effort to combat the scare stories and myths about the EU's threat to national identity.

"I believe there is a crisis of complacency among those who support Britain's EU membership," he said.

"Those who believe in the EU - in politics, in business, in the media, indeed in all walks of life - need to work harder and speak louder to explain both the benefits of membership by explaining in simple terms the reality behind the myths."

Straw condemned the British "caricature" of the EU that is "infused with a sense of defeatism and a profound lack of confidence".

"It assumes that co-operation with our neighbours comes at the price of dilution of our national character.

"It is based on the false premise that Britain is losing all of the arguments, that the battle for Europe's soul is going the way of those who support the vision of ever-closer union."

The foreign secretary said that much of the debate on the EU ignores Europe's strengths.

And he pointed to his visit to Iran alongside his French and German counterparts, which led to a deal on Tehran's nuclear programme, as proof of what can be gained from working together.

"This is the reality of a common foreign policy, in contrast to the mythology about the loss of sovereignty and is a demonstrable example of how our membership of the EU enhances our standing in the world."

While criticising eurosceptics, Straw accepted that pro-Europeans "should not pretend the EU is perfect".

But he criticised Conservative attacks on the planned EU constitution, saying the draft was "not going to end 1,000 years of nationhood".

"This is a myth perpetuated by those who have never reconciled themselves to Britain's modern role as a European power.

"They deal in myths and scares because they do not want the British public to see the EU for what it is - good for Britain."

Straw said that there is no threat to the Queen's status or the key defence role of NATO.

"Newspapers are, of course, entitled to take a view and to make a case. But they should try to win the argument on fact, not myth," he said.

"It is tempting to laugh off the more comical exaggerations. But that would be dangerously complacent.

"Because the cumulative effect of the scare stories is that the public hears and reads about the EU only when it can be presented as a problem."