Image copyright @JoeyMillar Image caption Visitors were welcomed to 'Free Camden' in a satirical response to Boris Johnson's comments

Boris Johnson's comparison of the Irish border with the boundaries of London's traffic congestion charge zone has been widely ridiculed.

The foreign secretary was speaking about the challenges Brexit will pose to moving goods over the 310-mile border without imposing checkpoints.

He said there was "no border between Islington or Camden and Westminster", and yet traffic fees were collected.

Comical comparisons of Camden and the border have sprung up on social media.

'The Cabinet clown'

Journalist Joey Millar replaced the word "Derry" with "Camden" in a doctored image of Free Derry Corner, an Irish nationalist mural which dates back to the outbreak of the Troubles in 1969.

The satirical group, Loyalists Against Democracy (LAD), posted a tongue-in-check caption onto an archive photograph of an Irish border checkpoint.

The criticism was not confined to social media.

In the House of Commons, Labour's Stella Creasy confused Chancellor Philip Hammond by asking him to set out the benefits of the government's plans for an apparent "customs union between Camden, Islington and Westminster".

Mr Hammond replied: "I'm sure when I go home and reflect on it, the deep meaning of that question will become clear to me", provoking other MPs to shout "Boris" across the chamber.

Media playback is unsupported on your device Media caption Boris Johnson compares Irish border with London boroughs

In Northern Ireland however, Irish nationalist parties were not amused.

Mr Johnson was referred to as the "clown" of the UK Cabinet by the leader of the Social Democratic and Labour Party (SDLP).

"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 Colum Eastwood.

"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."

'Frankly ridiculous'

The party has sent a memo to the Foreign Office outlining the problems posed by Brexit in an "effort to educate Mr Johnson".

Sinn Féin said Mr Johnson's remarks were evidence of "how the Tories view the north of Ireland as collateral damage in their Brexit agenda".

"The frankly ridiculous comments from British foreign secretary and arch-Brexiteer 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," said Sinn Féin MEP Martina Anderson.

Northern Ireland is the only part of the UK which will share a land border with a European Union member after Brexit.

The Conservative government has said the UK will leave the Single Market and the Customs Union when it leaves the EU, but the Irish government has warned that a so-called "hard border" would cause problems for both economies on the island of Ireland.

'Very efficient'

Several high-profile Brexiteers have argued that technological solutions can be deployed which would avoid the need for physical border posts or checkpoints.

Mr Johnson told BBC Radio 4's Today programme a hard border could be avoided by "very efficient facilitation systems".

"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," he said.

"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 to allow us to come out of the customs union, take back control of our trade policy and do trade deals."

'Already in use'

On the BBC's Daily Politics, Democratic Unionist Party MP Sammy Wilson came to the foreign secretary's assistance.

Mr Wilson pointed out that IT and electronic invoicing are already used to enforce regulations such as VAT and excise duty, which are different on either side of the Irish border.

Analysis - BBC NI economic editor John Campbell:

Automatic Number Plate Recognition (ANPR) cameras, the sort of technology Mr Johnson was referring to, have been continually talked about as one of the measures which could minimise disruption on the border.

The most comprehensive attempt to sketch out a technical solution for the border is a paper by the Swedish customs expert Lar Karlsson.

His study for the European Parliament described ANPR as a risk management tool which could be used in conjunction with other technologies.

However it did not suggest that it would totally eliminate the need for physical checks.

He wrote: "ANPR at unmanned border crossings would also allow the identification of commercial vehicles required to present themselves at manned border crossings."

The European Parliament also commissioned a report from the lawyer John Temple Lang which was more sceptical about the use of ANPR.

He suggested that "these devices could be easily put out of action, sabotaged, or destroyed, just as traditional customs posts could be".

He also wrote that if ANPR identified suspicious or non-compliant vehicles that was only the start of a process which would then involve physical checks.

"Any such system would necessitate a considerable degree of physical surveillance within the importing region, and could not be relied on to be effective to control smuggling."

Some London residents, past and present, were bemused by the comparison.

Labour MP David Lammy, who represents the Tottenham area of London, tweeted: "Did our Foreign Secretary really just compare the border between Northern Ireland and the Republic of Ireland to the border between Camden and Islington?

"God help us all this isn't just stupidity and ignorance but wilful recklessness."

'Extraordinary'

The Brexit spokesman for the Republic of Ireland's main opposition party, Fianna Fáil, also expressed disbelief at the comments.

"I lived in Camden for several years, and was never stopped crossing the 'border' to Islington," said Stephen Donnelly.

"I have, however, had military rifles pointed at me when crossing into Northern Ireland in the 90s.

"Suggesting these borders are the same is extraordinary."