Claims that pressure from Downing Street forced a senior business leader out of his post after he voiced support for Brexit have been dismissed by a Cabinet minister as "bizarre conspiracy theories".
John Longworth quit as director-general of the British Chambers of Commerce (BCC) following the controversy over his suggestion that the UK could have a "brighter" future outside the EU.
Number 10 has strenuously denied claims by Brexit campaigners that it put pressure on the BCC to act following Mr Longworth's comments at the group's annual conference on Thursday.
But advocates of UK withdrawal in the June 23 EU referendum were quick to see the hand of Prime Minister David Cameron behind the development.
Ukip MP Douglas Carswell said on Twitter: "Well done Downing Street. You got your man. This is what Project Fear looks like. Nasty people in Number 10."
And London Mayor Boris Johnson suggested Mr Longworth had been "crushed by the agents of Project Fear" and paid "quite a heavy price" for expressing optimism about the UK's future outside the EU.
But Defence Secretary Michael Fallon pointed to a statement by the BCC's president, Nora Senior, who said "no politician or interest group" had any influence on the initial decision of the BCC's board to suspend Mr Longworth and there were "no external factors" in his subsequent decision to quit.
Mr Fallon told Sky News: "The board of the British Chambers of Commerce have made it very clear that this was their decision, and there was no external pressure from anybody else.
"People who want to leave Europe - to vote No in the referendum - are seeing conspiracy theories everywhere now because they don't want to answer the basic question, which is 'If you leave Europe, where are you going? What are the new arrangements for trade? What is going to happen to the jobs that depend on Europe?'
"They have to start answering these questions instead of coming up with rather bizarre conspiracy theories that here the British Chambers of Commerce have flatly denied."
Ms Senior said the BCC's "neutrality in the referendum debate reflects the real divisions that exist in business communities across the UK".
"All representatives of the BCC have the right to personal and political views on the key issues of the day. However, they are not expected to articulate these views while acting in their professional capacity, as their views could be misconstrued as representing the position of the organisation as a whole," she said.
And the chief executive of the North East Chamber of Commerce, James Ramsbotham, said it was important for BCC leaders to respect the organisation's policy of not taking a side in the referendum, adding that he was not aware of any political pressure to force Mr Longworth out.
Mr Ramsbotham told the BBC Radio 4 Today programme that Mr Longworth had taken the right step in resigning, adding: "From the moment John was giving his speech it was very, very clear to everyone involved in Chambers of Commerce across the country that this would be the outcome.
A Number 10 spokesman insisted "no pressure" was put on the BCC to suspend its director-general.
"Given that 60% of BCC members say they want to stay in the EU, Number 10 was surprised to see the director-general of the organisation come out for Brexit," said the spokesman.
"We are clear no pressure was put on the BCC to suspend him. Of course Number 10 talks to business organisations regularly - but, to be clear, no pressure was applied. This decision is entirely a matter for the BCC."
Former Cabinet minister Liam Fox has said he may ask questions in Parliament to find out if ministers had any role.
The senior Tory told BBC Radio 5 Live's Pienaar's Politics: "I want an explanation as to what happened and I want to know if any part of Government - not just Number 10, any part of Government - was involved in putting pressure on the BCC to drop John Longworth, because I think that is inappropriate and I think if we don't get enough explanation we'll have to get a better one on the floor of the House of Commons."
Ukip leader Nigel Farage said: "I've met John Longworth, who is a thoroughly decent man. He has been treated appallingly for supporting Brexit."
And the party's MEP Roger Helmer said: "First the BCC comes under pressure to dump John Longworth. Then it comes under pressure to say that it didn't come under pressure."
Speaking to the Daily Telegraph, Mr Longworth declined to comment on suggestions that Number 10 put pressure on him to resign.
But he said he believed the Government could be "neutral" in the referendum campaign and was being "irresponsible" in stoking fears about the possible consequences of withdrawal.
"It is highly irresponsible of the Government of the country to be peddling hyperbole," Mr Longworth told the Telegraph. "It is all right for the campaign groups to do it because they are promoting a particular position.
"But the Government has to be responsible. And the fact of the matter is that there is a chance that the country will vote to leave.
"If the Government keeps peddling the line that it will be a disaster if we leave - which it actually won't be - they are going to put the country in a position where it will be damaged if we do."