John Longworth quit as director-general of the British Chambers of Commerce (BCC) following the controversy over his suggestion the UK could have a “brighter” future outside the EU.
Downing Street 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 Ukip MP Douglas Carswell responded to the announcement by tweeting: “Well done Downing Street. You got your man.”
He added: “This is what Project Fear looks like. Nasty people in Number 10.”
The BCC’s president, Nora Senior, insisted that “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.
Ms Senior said the BCC’s “neutrality in the referendum debate reflects the real divisions that exist in business communities across the UK”.
She added: “John Longworth and the BCC board recognise that John’s personal view on the referendum is likely to create confusion regarding the BCC’s neutral stance going forward.
“In light of this, John has taken the decision to step down as director general and his resignation has been accepted by the board with effect from March 6 2016.
“No politician or interest group had any influence on the BCC board decision to suspend Mr Longworth. His subsequent resignation was agreed mutually between Mr Longworth and the BCC board, and there were no external factors involved.
“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.”
Brexit-backing London mayor Boris Johnson earlier expressed his support for Mr Longworth as he suggested leaving the EU would be like escaping from jail.
Mr Johnson claimed the business leader had been “crushed by the agents of Project Fear”.
On BBC One’s Andrew Marr Show Mr Johnson hit out at the “negative” approach of the Remain camp.
“This is like the jailer has accidentally left the door of the jail open and people can see the sunlit land beyond,” he said.
“And everybody is suddenly wrangling about the terrors of the world outside. Actually it would be wonderful. It would be a huge weight lifted from British business.”
He added: “It is very sad that someone like John Longworth, who shares my view, who has great experience of British business and industry, should have paid quite a heavy price, it seems, for sharing that optimistic view.”
Former cabinet minister Liam Fox suggested he could 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.”
Business Secretary Sajid Javid and Chancellor George Osborne spoke at the BCC conference where Mr Longworth made his controversial speech.
A Number 10 spokesman said: “Given that 60% of BCC members say they want to stay in the EU, No 10 was surprised to see the director-general of the organisation come out for Brexit.
“We are clear no pressure was put on the BCC to suspend him. Of course No 10 talks to business organisations regularly - but, to be clear, no pressure was applied. This decision is entirely a matter for the BCC.”
Tory MP Conor Burns told BBC Radio 4’s Westminster Hour: “I think it’s a little bit of an overreaction. I think what he was saying is what a lot of people in small business are saying, in fact a lot of people in domestic business are saying.
“It’s worth remembering that only 6% of UK firms export into the EU area so I think his view was a moderate and legitimate one and I’m sorry they have reacted in the way they have.”