EU referendum: Sir Jeremy Heywood in legal warning

There is a danger of ministers being "hobbled" ahead of the EU referendum unless so-called "purdah" rules are relaxed, the country's top civil servant has said.

Sir Jeremy Heywood also warned the government could face legal challenges.

Ministers want to change the law so traditional pre-election restrictions on the civil service do not apply ahead of the referendum.

Some Eurosceptic Conservative MPs are unhappy at the change.

They say it will allow the government to use its resources to influence the outcome of the referendum, promised by 2016, in the weeks leading up to the vote.

Sir Jeremy Heywood said ministers would have to 'tread very carefully' in legal discussions

In an appearance before the Public Administration and Constitutional Affairs Select Committee, Sir Jeremy said "very worrying" legal advice suggested ministers could be subject to legal action unless they "tread very carefully" in EU discussions.

He added: "The sharpest case would be where a minister is negotiating on a highly contentious issue which everybody in this committee would agree was vital to the UK national interest, and felt hobbled by being unable to make any points about the importance of this to the referendum and so on, at precisely the moment when the whole of the British media and body politic is focused on that question."