Britain is no longer at the centre of the European Union under the leadership of David Cameron as it was under Tony Blair, a former president of the European commission has said.

José Manuel Barroso, who left his role as the most senior official in Brussels this year, said it was a “matter for reflection” that the UK was not at the heart of decisions any more because of anti-EU sentiment within the Conservative party.

In a further swipe at Britain’s status in the world, the Portuguese politician said the US president was now more likely to call the German chancellor than the UK prime minister if he wanted to get European countries on board for international action.

He said Britain would be much more influential today if it had a more positive attitude towards the EU rather than constantly pursuing a “defensive agenda” of trying to get exceptions and special treatment.

Speaking on BBC Radio 4’s World at One, Barroso said: “I’ve worked, and I think I’ve established good relationships, personal relationships, with Tony Blair, Gordon Brown and now David Cameron, so I very much respect them, but it’s quite clear that the current prime minister has a difficult relation with the European Union. I think it’s not personal – I really believe that’s because of the pressure in his party that exists very strongly against the European Union.

“I see David Cameron as basically a very pragmatic leader – someone that certainly wants to defend the interests of his country, certainly, as the previous prime ministers have done. But while with Tony Blair, Britain was really playing a very important role in the European Union – they were at the centre of decisions – today, this is no longer the case, and I think this is a matter for reflection.”

He added: “The American president, if he wants to get European countries on board, I think the first call he makes is to the chancellor of Germany, no longer to the British prime minister, and this is new. Frankly, it’s not very appropriate for Britain to leave the very important position Britain has, or at least had, at the centre of the European Union.”

Barroso suggested that Cameron had ruined the UK’s position within Europe even if future leaders wanted to take a different approach. “Unfortunately because of some exceptionalism that the current leadership in Britain wants to consolidate regarding the European Union, I think the opportunities for a more positive, proactive leadership have been, to some extent, spoiled,” he said.

Since becoming prime minister, Cameron has increased his criticism of the EU under pressure from Nigel Farage’s anti-EU party Ukip and the right of the Tory party. Last year he promised to hold a referendum on Britain’s membership of the EU before the end of 2017 if he is still in power. He has maintained that he would refer Britain to stay in a reformed EU, but he and other senior ministers have hinted that they could lead the UK out of the alliance if they do not get their way in renegotiations.

Labour has long argued that this approach is leaving the UK isolated within the EU, with Douglas Alexander, the shadow foreign secretary, accusing the prime minister of “burning bridges with our EU allies when he should have been building alliances”.

Pat McFadden, Labour’s shadow Europe minister, said: “The stance adopted by David Cameron, driven by weakness in the face of his Eurosceptic backbenchers, is not serving Britain’s interests well. We need a more confident approach where Britain plays a leading role in Europe.

Britain has already had considerable success in shaping the EU, and we can do so again in the future. The marginalisation that Mr Barroso speaks of is a result of weak leadership from the prime minister and an approach that puts short-term management of the Conservative party ahead of the strategic interests of the country.”

Henry Smith, a Conservative MP, hit back at Barroso’s comments, saying he was “harking back to the days of Tony Blair and Gordon Brown, who rolled over to his EU demands time and time again”.

Smith said: “David Cameron is a prime minister who has stood up for Britain’s interests in Europe and will continue to do so, no matter what feathers are ruffled in Brussels. With the fastest-growing economy in Europe, Mr Barroso should perhaps look to the UK for advice and inspiration rather than lecturing us from a sedentary position.”