'You couldn't make it up': Good Friday Agreement negotiator Reg Empey reacts to fact that the manager of republican rap crew Kneecap is a former Irish diplomat

He then became an advisor to Ireland's mission to the United Nations before leaving in 2014.

Sir Reg Empey has told the News Letter he is “horrified” that a former Irish government mandarin is now promoting the trio, who rely on violent republican iconography to promote their songs.

This has included chanting “Brits out” from the stage, accusing the Queen of overseeing “wars and deaths of millions [from] Belfast to Baghdad, Libya to the Malvinas”, tweeting out a picture of a guillotine and calling for a “united front against the King” on the eve of the coronation, and unveiling Kneecap-branded murals: one of a burning PSNI Land Rover along with the message “RUC not welcome”, and another saying “England get out of Ireland” with a balaclava motif next to it.

• Troubles victims activist rounds on media for attempting to 'mainstream' west Belfast rap trio Kneecap

Sir Reg is a UUP peer who was in charge of his party's negotiations on Strand One of the 1998 Good Friday deal (for which his leader David Trimble won the Nobel Peace Prize).

"It's about as far away from being diplomatic as it's possible to get,” said Sir Reg.

"You couldn't make some of that up.

"It just brings back the worst memories. People who I feel are probably affected most are victims, who are seeing the type of thing that led to their loved ones' being killed being sort of glorified in some kind of a way.

"It sort of ties in with recent events and sporting things where people have been shouting 'up the Ra' and that sort of thing.”

He said in those cases, as in the case of Kneecap’s members, “those people would have been born probably after the Agreement... and would've had no memory or experience of the Troubles” directly themselves.

“To be honest I'm horrified by it,” he concluded.

"I think that the fact you've a former Irish diplomat who would know perfectly well I have to say the implications of all of this.

"There'd be no secrets or surprises as far as that person is concerned because he would know how people were affected and how they would be affected by this.”

The News Letter asked Mr Lambert about Sir Reg’s comments.

He said: “There’s journalism and then there’s the News Letter Belfast [sic]. Nobody from Kneecap will be providing comment to your ‘paper’, ever.”

Kneecap themselves have previously said “we don’t want to be fighting or advocating violence – we want people to be thinking,” and member Moglai Bap recently commented that: "There's a lot of playfulness and a lot fun and craic, if you're offended by it then you're just not getting the joke… we didn't establish sectarianism and we're not fuelling it either.”

Mr Lambert himself told RTE this week: “I think controversy is subjective, actually. Especially in the north, people love to be outraged.

"Take the idea of DJ Provai [pronounced Provie]; I think it’s quite satirical in terms of wearing a green, white and orange balaclava.”

On the subject of the group’s burning police vehicle, he said: “I think Naomi Long came out, the Minister of Justice, saying this was stoking sectarian tensions, and the lads’ response to me was perfect.

"They said: ‘Well if you ask somebody on the other side of that wall how they’d like to see an RUC jeep, they might say the same thing’.

"So the lads are totally non-sectarian. The song ‘Get Your Brits Out’ is about a night out with the DUP.”

As well as managing Kneecap, Mr Lambert is currently the chief operating officer of Dublin football club Bohemian FC, an executive committee member of the Football Association of Ireland (the southern equivalent of the IFA), and his LinkedIn profile also lists him as the owner of a Dublin deli and former "business development manager" for smoothie brand "Innocent".

Mr Lambert is a heavy user of Twitter, where he describes himself as "former diplomat @UN".

The former diplomat’s activity in the past fortnight or so includes retweeting a speech by Bernadette Devlin / McAliskey, the founder of the INLA's political wing the IRSP, in which she attacked Irish politicians going to meet the US president on St Patrick's Day, saying: "Who in their right mind, on the national day of a country that freed itself from oppression, would go to America and hand the bastard a bunch of feckin' shamrocks?"

Mr Lambert also tweeted that "now we have two former ministers for justice who are remarkable apologists for Israel’s genocide", and re-tweeted an article from the Irish News in which People Before Profit MLA Gerry Carroll attacked Kneecap's critics, saying "Britain’s ruling elite have no business condemning young people in areas like west Belfast, which were decimated by its military”.