Sir Richard Branson has warned small businesses are at far greater risk from Brexit than larger firms, and could be clobbered with a costly amount of bureaucracy once Britain leaves the EU.
The billionaire tycoon told the Press Association the impact of Brexit could be bigger than "any small businesses ever imagined" and it is "critical" they continue to enjoy access to EU markets.
"Small businesses are likely to suffer more than big businesses from Brexit and that's because big businesses have overseas earnings in dollars, and as the pound goes down they can cushion themselves.
"The massive question is, will small businesses have access to Europe in the way that they had in the past?
"There is a danger that if the Brexit negotiations go wrong, the bureaucracy could be far, far greater than any small businesses ever imagined.
"Importation duties, the exportation duties, this big market being made much more inaccessible, it is critical."
The Virgin boss was an outspoken Remainer prior to last year's vote, and over the weekend said a hard Brexit would be a "disaster" for the UK and could warrant a second referendum.
Sir Richard has also helped pay for the office used by Gina Miller, the businesswoman whose legal action forced a parliamentary vote on withdrawal from the EU.
She launched the Best For Britain crowdfunded initiative to influence the result in marginal seats last week.
He added it is vital government negotiators "realise the importance of us being able to trade within Europe" and that small firms are not "precluded" from the EU market in any deal that is struck.
"That's the most important thing, that that market is not precluded for small businesses and that it doesn't become cumbersome, bureaucratic and expensive as it did before the European Union was formed.
"If we can get rid of that thing hanging around our necks, I think small businesses can continue to flourish as they've been doing for a long time."
Prime Minister Theresa May has confirmed Britain will leave the single market and the customs union post Brexit, in contrast to the desire of most British businesses.
However, Sir Richard said he will not take sides ahead of the election on June 8.
"It's invidious for business people to get involved in party politics.
"Business people should talk out on issues but not get involved in backing political parties.
"It's invidious for the businessman and invidious for the party itself," he added.
The businessman was speaking on the sidelines of the launch of Voom, a Virgin initiative that allows budding entrepreneurs to pitch their ideas and give them the chance to win funding and other support.
Sir Richard said Voom aims to challenge people to "put aside their fears" and pitch business ideas that are going to make a positive difference to lives.