Boris Johnson has dismissed concerns that leaving the customs union could lead to a hard Irish border by comparing travel between the Republic and Northern Ireland to crossing London boroughs, in an apparent reference to the congestion charge for drivers, which does not require checks on the road.
The Foreign Secretary told BBC Radio 4's Today programme: "We think that we can have very efficient facilitation systems to make sure that there's no need for a hard border, excessive checks at the frontier between Northern Ireland and the Republic.
"There's no border between Islington or Camden and Westminster, there's no border between Camden and Westminster, but when I was mayor of London we anaesthetically and invisibly took hundreds of millions of pounds from the accounts of people travelling between those two boroughs without any need for border checks whatever."
SDLP leader Colum Eastwood said Mr ohnson needs to ‘come back down to earth’
He also challenged Johnson to visit the border "to see the scale of the challenge himself".
“When Boris Johnson decides to come down from the other planet that he clearly inhabits, he should visit the Irish border and see the scale of the challenge we’re facing with his own eyes before making further pronouncements," said Mr Eastwood.
“In an effort to educate Mr Johnson, the SDLP has issued a memo to the Foreign Office detailing the difficulties with a hard border and the realities faced by people, businesses and communities here.
“It’s easy to characterise Boris Johnson as the cabinet clown but he carries an immense responsibility and has significant influence in the Brexit negotiations. Trivialising the very serious concerns relating to Ireland displays a dangerous ignorance that must be challenged.”
The Foreign Secretary said: "It is a very relevant comparison because "there's all sorts of scope for pre-booking, electronic checks, all sorts of things that you can do to obviate the need for a hard border to allow us to come out of the customs union, take back control of our trade policy and do trade deals."
Sinn Féin MEP Martina Anderson said the comments "highlight how the Tories view the north of Ireland as collateral damage" in their Brexit agenda.
Martina Anderson said: "The frankly ridiculous comments from Boris Johnson that there is no border between council boroughs in London and that somehow that is comparable to the situation in Ireland shows how out of touch with reality he actually is.
"He, like many of the Tory cabinet, have so little comprehension of what happens beyond the M25, let alone what the reality is on the ground in Ireland.
"It may have escaped his attention that Ireland is already partitioned and that the reckless Brexit agenda pursued by his government has the potential to copper fasten and increase the huge damage that was done to the island and its people by partition. "