Colin Stanbridge, CEO of the London Chamber of Commerce and Industry, said exports were the key to a successful Brexit and Britain would fail without focus.
Speaking on CNBC, Mr Stanbridge said the party leaders needed to shift their attention and concentrate on foreign markets.
Discussing last night’s leadership debate, he said: “I don’t think I heard anything last night about exporting.
“We do trade missions, we know how difficult it is to persuade companies to go to long haul markets.
Colin Stanbridge said Theresa May and Jeremy Corbyn needed to consider exports for Brexit to work
Exporting is going to be the way we survive and make a success of Brexit
“I would have thought that each of the leaders would be talking about ‘well this is what we’re going to do.
“When we’re out of the EU, these are the markets and this is the help we’re going to give.
“Exporting is going to be the way we survive and make a success of Brexit.
“I’m sad that the politicians don’t seem to be interested at all in what’s really a very important subject.”
May meets Juncker and Barnier at Number 10 Wed, April 26, 2017
Theresa May hosted European Commission President Jean-Claude Juncker and chief negotiator Michel Barnier at Downing Street for the first face-to-face talks since she triggered the two-year process of withdrawing from the EU
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Prime Minister Theresa May greets European Commission President Jean-Claude Juncker ahead of a working dinner at 10 Downing Street, London
Asked how important a Brexit deal was, Mr Stanbridge added: “We have to have a deal, there’s no doubt about it.
“I think that behind the scenes, when you talk to civil servants and politicians, they accept ‘yes of course, you’ve got to say we’re able to walk away’, but walking away is a deal of some description.
“There has to be something, there has to be a deal and we have to accept this this is going to take a lot more time than the two years.
“Even if we walk away, we will still be talking to the EU because we need open skies, we need all sorts of things for Europe to function and for the UK to function.
“There’s got to be a deal and there will be a deal.”
Meanwhile, Britain's divorce bill for leaving the European Union will be linked to talks on a future trading relationship, eurocrats revealed for the first time on Tuesday in a boost to Mrs May.
EU Commission guidelines show that the “schedule of payments” – the terms under which the UK will pay the Brexit fee – will not be thrashed out until the second phase of the talks.
Eurocrats had previously insisted that the issue of Britain’s financial obligations must be done and dusted before they were prepared to move onto talking about future economic ties.