Boris Johnson has been condemned for comparing the problem of the Northern Irish border after Brexit to the London congestion charge.
The Foreign Secretary, who served two terms as Mayor of London, was accused of being on "another planet" after drawing a link between the bloody conflict in Northern Ireland and the boundary between the boroughs of Camden and Westminster.
The government has proposed to stop a hard border being created after the UK leaves the EU single market and customs union by using technology, including remotely operated cameras, to perform customs checks if a trade deal isn't agreed between London and Brussels.
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London's congestion charge operates on similar technology, which photographs vehicle number plates.
Speaking on the BBC's Today programme, Mr Johnson said: "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.
"For people listening, 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."
Mr Johnson added: "I think it’s a very relevant comparison, because there is 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."
Shadow Northern Ireland Secretary Owen Smith said the comparison was "typically facile and thoughtless", and it was condemned by politicians at Westminster and in Northern Ireland.
SDLP leader Colum Eastwood tweeted: "When @BorisJohnson decides to come down from the other planet that he clearly inhabits he's welcome to come and actually visit the Irish border."
Liberal Democrat Northern Ireland spokesman Alistair Carmichael said the comments show "this country is not in safe hands.”
"Once again the Foreign Secretary has shown why he shouldn’t be allowed out of the house to talk about foreign affairs," Mr Carmichael said.
“He has revealed a complete lack of understanding of the complexities and history of the Northern Irish border. It is one of the major outstanding issues of Brexit negotiations and one of our most senior Cabinet Ministers hasn’t even bothered to read his briefing notes.
“Peace was brought to Northern Ireland as a result of cooperation across the parties in Britain and Northern Ireland as well as between the UK and Ireland. Comments in recent days questioning that consensus shows that there is nothing that the Brexiteers will not do to achieve their ruinous end."