The President of the European Commission warned UK Prime Minister David Cameron that he is being too complacent with how much opposition there may be in the run up to the EU referendum.

In a speech at Chatham House, Jose Manuel Barroso said that pro unionists should make more of a "positive" case for Britain staying within the European Union because he thinks that UK politicians haven't fully prepared for potential opposition towards remaining part of the union.

"It is an illusion to believe that space for dialogue can be created if the tone and substance of the arguments you put forward question the very principle at stake and offend fellow Member States. It would be an historic mistake if on these issues Britain were to continue to alienate its natural allies in central and eastern Europe when you were one of the strongest advocates for their accession," he said.