Media playback is unsupported on your device Media caption Boris Johnson: "Nobody has been gagged, I was only made aware of this edict very late last night"

Boris Johnson says an email telling his senior staff to back him over the EU referendum has been withdrawn.

The London mayor, who is campaigning to leave the EU, said the memo to deputy mayors and senior advisers was "a cock-up, and not something I agree with".

It told them to "either advocate the mayor's position or otherwise not openly contradict it" when not at work.

The email was sent 24 hours before Mr Johnson accused pro-EU campaigners of trying to gag opponents.

It was sent by his chief of staff, Edward Lister.

"Nobody has been gagged, 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," Mr Johnson said.

"All I can say is it obviously hasn't been operative because my advisory team take a very different view from me."

'Project fear'

He added "it's a cock-up and not something I agree with", saying he was in favour of allowing - in the words of former Chinese leader Chairman Mao - "a hundred flowers to bloom".

The mayor said his staff were "producing all sorts of views completely different from my own", adding that the memo had been "wiped from the page of history".

BBC political editor Laura Kuenssberg said while Mr Johnson was happy for his senior staff to argue for the UK's EU membership outside work, he was not able to withdraw statutory advice saying they cannot contradict him when carrying out official duties.

David Cameron and the government are campaigning to remain in the EU in the 23 June referendum. Government ministers have been told they can back either side, but conditions apply and they are not allowed to use Whitehall resources to help their campaigns.

Image copyright Other Image caption The e-mail was circulated to deputy mayors and senior advisers in City Hall

The City Hall instruction, in an email sent on 4 March, was circulated before Mr Johnson accused pro-EU campaigners of trying to silence those arguing for Brexit who he claimed were being "crushed by the agents of Project Fear".

The email, revealed by Laura Kuenssberg, says it includes an attachment offering formal advice from the City Hall management team on what the Greater London Authority (GLA) can and cannot do during the referendum.

'Inclusive debate'

The email highlights that the advice says: "Boris is entitled, as mayor, to adopt a public position on this issue and then, as with all other mayoral policies, to receive support from GLA officers in relation to that policy position.

"The advice also makes clear that GLA officers can, when not at work, express personal opinions (which be contrary to the mayor's views). Whilst this is the formal position for you also, I would expect, given your roles, you either to advocate the mayor's position or otherwise not openly contradict it."

Image copyright PA Image caption One of Mr Johnson's deputy mayors has said the situation is confusing

The email also notes that because it is a referendum and not an election "you are all able to be involved in the campaign as you may wish (but without using the authority's resources for your personal activities)."

The mayor's official spokesman said: "The mayor is relaxed about any of his team of advisers in a personal capacity campaigning for or supporting either side in the EU referendum.

"He wants to see an open and inclusive debate, and recognises that some of his advisors have differing views to those he holds.

"In his role as chief of staff Ed Lister advised the team that as official mayoral policy is now to support the case for leaving the EU they are requested to support that position when undertaking official City Hall business."

'Confusing'

The mayor's office said the advice was "in line with that issued by the GLA's statutory officers".

Although his deputy mayors and senior advisers are political appointees, they are technically officials of City Hall so not subject to the same rules as elected representatives.

Stephen Greenhalgh, the deputy mayor for policing who backs the UK's continued EU membership, said allowing officials to campaign freely in their own time was right but the situation was "terribly confusing" for those working in City Hall.

"There's an official mayoral policy that advocates Brexit and the London Assembly are advocating to remain so that means half the officials inside that building are supporting a contrary official position from the other," he said.

The Britain Stronger in Europe campaign released a statement from London MPs Tom Brake and Chuka Umunna, accusing Mr Johnson and Leave campaigners of "trying to have their cake and eat it".

"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," they added.