After a couple of night shifts, he flies back home – until the next weekend, when he does the same again.

Cunningham, 28, has always wanted to be in the police, but his attempts to join the force in Scotland have been turned down.

Police Scotland says he cannot become a police officer north of the border because of “third-party risk”, which Cunningham said he believed related to the fact three of his uncles have criminal records.

Colin Cunningham always wanted to be in the police, but his attempts to join the force in Scotland have been turned down.

“I’ve been trying to apply for the police since I was 18,” he said. “The first time I applied it came back as ‘failed vetting due to third-party risk’. I got a meeting with the vetting unit and they were saying it’s not me – I’ve never been in trouble – but there was a high risk because of a person who has a criminal record in the family.

“Due to data protection, they won’t say who it is, but none of my immediate family has been in trouble. Three of my dad’s brothers have criminal records, but I’ve not seen them since I was a child.

“When I said that, they just said ‘blood is thicker than water’.”

Vetting policies are different south of the Border, so Cunningham decided to apply to the Met and was accepted. “I was honest with them,” he said. “When I put in my application form I wrote a letter with it saying I have applied to Police Scotland on these many occasions and been rejected, but they said it would have no bearing on my application – and when the vetting came back it was absolutely fine.”

Cunningham completed the training and has been serving as a special constable for a year now. He makes his regular trips down on a Friday, working Friday and Saturday night shifts and returning home on Sunday morning, ready for his week’s work running a cleaning company.

He said each weekend round trip, plus accommodation, cost him around £200. “Because it’s something I want to do, you can’t put a price on that,” he said.

Cunningham does not want to move down to London permanently because his fiancée is reluctant to relocate.

He puts in a new application to Police Scotland every six months. “I’ve never had another career path in mind, so it’s devastating,” he said.

Liberal Democrat MSP Alex Cole-Hamilton raised the case in the Scottish Parliament recently of Jamie Duff, who was rejected by Police Scotland because of his estranged father’s criminal record.

Justice secretary Humza Yousaf said recruitment was an operational matter for the police.

But Cole-Hamilton said Cunningham’s experience reinforced the case for a rethink of the rules.

He said: “It’s clear that if the Met imposes no such barrier to joining the police force in England, then the argument by Police Scotland that criminal associations could expose the police service to corruption or infiltration by organised crime carries far less weight.”

Chief Superintendent Mark Hargreaves said Police Scotland’s vetting procedures closely followed the practice of UK police forces.

Police Scotland rules force Fife officer to work in London