Fianna Fáil's Stephen Donnelly said "suggesting these borders are the same is extraordinary"
British Foreign Secretary Boris Johnson has faced criticism after comparing the Irish border to the ones between different boroughs in London.
Mr Johnson made the remarks during an interview on BBC Radio 4.
He argued: "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... 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 was referring to the London congestion charge - a fee paid by motorists who enter certain areas of the city centre during peak hours.
When pressed about the comparison by presenter Mishal Husain, Mr Johnson insisted: "It's 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."
The remarks faced a swift backlash from politicians in both the UK and Ireland.
Fianna Fáil's Brexit spokesperson Stephen Donnelly said: "I lived in Camden for several years, and was never stopped crossing the 'border' to Islington.
"I have, however, had military rifles pointed at me when crossing into Northern Ireland in the '90's. Suggesting these borders are the same is extraordinary."
British Labour MP David Lammy described the comparison as 'wilful recklessness':
Did our Foreign Secretary Boris Johnson really just compare the border between Northern Ireland and the Republic of Ireland to the border between Camden and Islington on @BBCr4today just now? God help us all this isn’t just stupidity and ignorance but wilful recklessness #r4today— David Lammy (@DavidLammy) February 27, 2018
The comparison was also widely mocked on social media:
Nobody wants to see this again on the Camden / Islington border. pic.twitter.com/SzjIGIjloB— Harry Cole (@MrHarryCole) February 27, 2018
The EU is due to publish its proposal for a draft Brexit agreement tomorrow, which is set to detail the EU's preferred legal solutions to avoid a hard border.
Speaking today, the EU's chief Brexit negotiator Michel Barnier said significant "points of disagreement" remain between the two sides over any potential transition deal.