Angus MacNeil was put on the spot but said British voters would see Brexit in a “very different light” once the UK’s “empire dream vanished”.
He said: “Theresa May’s rhetoric of her looking for the best deal for Britain of course overlooks the fact that the United Kingdom currently has the best deal possible that it could have.
“It’s got no trade barriers at all with the European Union 27, which it will have after it leaves the European Union.
“It also raises the question of exactly what is the policy in Ireland and it looks like the UK will be imposing, or helping to impose, a hard border across the island of Ireland.
“The number of areas of rhetoric that the Prime Minister has, whether it’s the best deal or no border in Ireland, actually seem very hollow when they’re put to the cold light of day.”
Asked if he wanted Brexit to fail, Mr MacNeil added leaving the EU would be seen in a “very different light” in future and would “raise trade barriers”.
He said: “The exercise of Brexit, far from being an exercise in free trade, is an exercise in the very opposite of that.
“Brexit is increasing trade barriers, Brexit is making it more difficult for people, for commerce and for prosperity to occur in years to come.
“I think once the empire dream of the UK, once that vanishes and goes, perhaps Brexit will be seen in a very, very different light.
“I think more people are waking up to what Brexit actually means, it means the raising of trade barriers.”
David Davis has confirmed parliament will have a vote on the final Brexit deal before Britain leaves the EU.
Giving a statement before parliament this afternoon, the Brexit Secretary confirmed the Government intends to give MPs a say on our departure from the EU.
But if they reject the deal the Government strikes with the EU, Britain will instead leave the bloc with no deal, he confirmed.
Mr Davis said: “Parliament will be given time to debate, scrutinise and vote on the final agreement we strike with the European Union.
“This agreement will only hold if parliament approves it.
“This will include the contents of the Withdrawal Agreement, that includes issues such as an agreement on citizens’ rights, any financial agreements, and agreements on an implementation period by both sides.”
MPs will therefore have the power to approve or veto a comprehensive Brexit deal.
The move is intended to put to rest fears of a Brexit deal that would be bad for Britain being brought in without scrutiny.