Boris Johnson has condemned one of the UK's biggest business groups after it suspended its director general for suggesting the UK could have a brighter future outside the European Union.
The Mayor, who is a prominent Brexit backer, said it was "scandalous" that John Longworth had been suspended by the British Chambers of Commerce (BCC).
The BCC is remaining neutral in the referendum campaign and Mr Longworth stressed he was giving his personal opinion as he used his keynote speech at the organisation's conference to say the UK might be better off outside the EU.
Mr Johnson claimed that Mr Longworth had become a victim of "Project Fear" - the label used by Brexit campaigners to criticise the tactics used by David Cameron and his allies backing a Remain vote.
Number 10 strenuously denied any involvement in the BCC's decision to suspend Mr Longworth.
Mr Johnson said: "It is absolutely scandalous that John Longworth has been forced to step aside.
"This is a man who reached the conclusion - after long reflection and a lifetime's experience of business - that it would be better to vote Leave.
"His verdict reflects the reality - that the EU has changed out of all recognition from the Common Market that this country joined.
"He speaks for the many small and medium sized businesses - the lifeblood of the economy - who cannot understand why they should comply with more and more regulation, over which this country has no democratic control.
"Only 5% cent of UK firms do business with the rest of Europe, and yet they must obey 100% of EU legislation.
"The British public deserve to have the facts put before them. They deserve a proper debate.
"It cannot be right that when someone has the guts to dissent from the establishment line, he or she is immediately crushed by the agents of Project Fear."
The Sunday Telegraph said a friend of Mr Longworth claimed Downing Street had "bullied" and were "putting pressure" on BCC board members to suspend their director-general.
But a No 10 source said: "This is simply not true. This is a matter for the BCC. No pressure was put on the BCC to suspend John Longworth."
In his speech on Thursday, Mr Longworth said "the very best place for the UK to be is in a reformed EU" but "I have come to the conclusion that the EU is incapable of meaningful reform, at least in the foreseeable future".
He acknowledged that although there would be uncertainty from a Brexit, "the long-term risks of staying in the EU are likely to be as daunting as the short-term risks of leaving" and "the dynamism and resilience of the City of London and the UK business sector suggest to me that, in the long run, we have the capacity and capability to create a bright - if not brighter - economic future outside of the EU".