Boris Johnson
Mayor of London was forced to claim that none of his City Hall staff had been gagged over the vote.=Reuters

The bombastic mayor of London, Boris Johnson, has seemingly become the unelected and unofficial head of the Brexit campaign ever since he dramatically declared for 'leave'. The problem for the ambitious Conservative MP is that he has faced ever more scrutiny from the press and political rivals, including pro-EU Prime Minister David Cameron.

Johnson's latest "cock up", as he put it, was a memo sent to top City Hall staff ordering them to back his Brexit position or remain quiet on the issue. The warning was apparently authored by Johnson's chief of staff Sir Edward Lister, and stressed that staffers could air a personal opinion on the 23 June ballot, but the use of the authority's resources was out-of-bounds.

The memo was leaked to the BBC and the broadcaster duly published it, triggering a sharp U-turn from Johnson, who denounced the document.

"Nobody has been gagged," Johnson told reporters on 8 March. "I was only made aware of this edict very late last night and it ceased to be operative as soon as I was made aware of it. I had no knowledge about it. It's a cock-up, I perfectly accept that.

"My staff and my team have complete freedom to say what they want. They already are and have been for several days."

'Asset not a burden'

The gaffe comes after Johnson's rough time on BBC's One Andrew Marr Show, which was branded "disastrous" by Eurosceptic economist Andrew Lilico.

But Grassroots Out (GO), one of the groups vying for the Electoral Commission's Brexit campaign designation, denied that Johnson was becoming a burden for the 'leave' cause.

"Johnson is obviously a huge asset to the Brexit campaign, he speaks to sections of society that other politicians do not and to win this campaign we need a collection of voices, ranging from Johnson to Nigel Farage, to David Davis to Kate Hoey," a GO spokesperson told IBTimes UK.

A spokesman for Vote Leave, the other group competing for the 'leave' designation, said: "Boris is one of the most popular politicians in the country, and when Andrew Marr allowed him to speak, he made an effective and positive case for Voting Leave."

The Eurosceptics' sentiments seem to be supported by the latest leadership survey from the Conservative Home blog.

The poll put Johnson on 33%, Justice Secretary Michael Gove on 20% and former Defence Secretary Liam Fox on 18%. The top Tories all have something in common – they back a Brexit.

Chancellor George Osborne and the Home Secretary Theresa May scored 11% and 10%, respectively. The cabinet ministers are backing a 'remain' vote at the EU referendum.

But despite Johnson's positive approval ratings among the Tory faithful, Britain Stronger in Europe were quick to seize on the memo story.

Brexit designation competition explainedIBTimes UK

Labour MPs Tom Brake and Chuka Umunna, in a joint statement, said: "Those at City Hall will be left thoroughly confused.

"Boris and his staff should immediately release new guidance making it crystal clear that everyone has the right to campaign for Britain to stay in Europe because they believe that is best for London.

"Boris and Leave campaigners were trying to have their cake and eat it. Boris has U-turned sharply and realised it was completely inappropriate to muzzle deputy mayors and senior advisers from speaking up for London.

"Just because Boris has turned his back on our capital in his last act as mayor doesn't mean everybody else in City Hall should be forced to follow suit. Our EU membership is vital for London's economy, bringing jobs, lower prices and investment to our capital city."

The latest opinion poll from YouGov, of more than 1,600 people between 2 and 3 March, put 'remain' three points ahead of 'leave' (40% versus 37%), with 18% of respondents undecided.