Arron Banks was being questioned by a parliamentary committee after claims he held undisclosed meetings with Russian officials at around the time of the 2016 EU referendum.
The co-founder of the Leave.EU campaign group – and friend of Nigel Farage – admitted to MPs he “led people up the garden path” during the referendum campaign and used “alternative methods” to influence the Brexit vote.
But he abruptly left the hearing after more than two and half hours, saying it had over-run and he had another appointment.
“Sorry I have to insist,” Mr Banks said.
“I was told a certain time and we’ve got a lunch appointment we don’t want to be late for.”
Leave.EU communications chief Andy Wigmore, who was also appearing before the committee, added: “You can join us if you want. We’ll be in the House of Commons’ bar.”
When committee chairman Damian Collins asked for five more minutes, Mr Banks replied: “No, you said 20 minutes and now we’ve run way past 20 minutes.
“I’m sorry but I’m afraid it’s time to go. But I think we’ve been as open as we could be with the issues you’ve raised.”
When Mr Collins again pressed for five more minutes, Mr Banks responded sternly: “No, no, no – the word is ‘no’.”
Mr Banks, who gave £9m to the Leave.EU campaign, was appearing at the committee after the Sunday Times reported he had repeated contacts with Russian officials during the referendum campaign and afterwards.
The newspaper said he had discussed a potential business deal involving six Russian gold mines with ambassador Alexander Yakovenko after being introduced by a suspected Russian spy.
Mr Banks told MPs that no money from his overseas business interests formed part of his political donations and he was “crystal clear” about the rules.
“I pay a shed-load of tax, probably more than the entire committee put together,” he said.
“I’m not going to be lectured about my business interests. I structure everything legally.”
Mr Banks joked that he was portrayed as an “evil genius with a white cat that controls the whole of western democracy”.
“Clearly that’s nonsense,” he said.
Appearing before the MPs’ committee investigating so-called “fake news”, Mr Banks confirmed Leave.EU held talks with controversial data firm Cambridge Analytica and intended to use its services if it had been selected as the official Leave campaign – which it was not.
Setting out the campaign’s approach, Mr Banks said: “We were not above using alternative methods to punch home our message or lead people up the garden path if we had to.”
He acknowledged giving the Russian ambassador the telephone number of Donald Trump’s transition team before the president won the US election.
Meanwhile, Mr Wigmore told MPs he initially met Russian officials at a UKIP conference to talk about bananas in his role as a diplomat for Belize and had since met Russian figures “many times”.
He said: “I was trying to find investors to look at perhaps buying a banana farm which had got into trouble because of its owner… and as a consequence Belize couldn’t sell its bananas in places like the United States or the United Kingdom.”
Asked if Leave.EU had received any money from the Russian government, Mr Wigmore replied: “No. Nyet.”