Two parking wardens have been arrested at Camden’s parking offices on suspicion of having fake passports – amid claims that illegal immigrants are commonplace in the service.

The incident came to light after a former warden approached the Ham&High alleging that illegal workers – mostly from Nigeria – are employed by private firm NSL which runs Camden Council’s parking service.

An NSL source said it had dismissed several illegal immigrants, following tip-offs from former parking warden Michael Onumajuru, who was sacked by the service in August.

The Ham&High understands that two men were arrested at NSL central Camden offices in Guilford Street on August 8 after Mr Onumajuru and others in the parking service drew up a list of illegal workers.

A police spokesman said one of the men was arrested for holding a fake passport and on suspicion of entering the country illegally.

He was questioned, bailed and given an official caution.

She added that they had insufficient evidence to prosecute the second man.

NSL has launched an investigation into allegations of illegal immigrants working across its Camden bases.

An NSL spokesman said: “NSL has the best system for checking the right to work of any company in the UK.

“We do, of course, need to remain vigilant. The law is quite clear and we need to ensure that everyone who works for NSL has the right to work in the UK.

“To do this we regularly do spot checks for example, to ensure that no one whose visa has expired remains in their post.”

Mr Onumajuru, who worked for NSL from 2008, is filing for unfair dismissal after claiming he challenged his superiors over the widespread practice of employing illegal immigrants from Nigeria. NSL denies the claims.

In documents seen by the Ham&High, NSL claims Mr Onumajuru ignored instructions as to where he should work and as such committed an “act of gross misconduct” and “insubordination”.

Mr Onumajuru, 49, said senior staff had tried to have him sacked last year.

He said: “They made false allegations against me because they wanted to get rid of me because I was trying to make the council aware of ‘illegals’ working in the service.

“It’s not fair on the illegal immigrants who work there because they have no legal protection.”

The revelations come at a time when the UK Border Agency (UKBA) faces “bribes for visas” allegations.

A senior UKBA employee is due in court this week over claims he accepted bribes for allowing Nigerians to enter the country illegally.

Mr Onumajuru, originally from Nigeria but with a German passport, claims that most of the immigrants assume false names in order to work in the UK.

The UK Border Agency is working closely with NSL over staffing issues. In a January operation at an unknown NSL office in London, a member of NSL staff was arrested.

An NSL spokesman said: “We sometimes seek the help of the police or the UK Border Agency if we see anything that gives us cause for concern.

“We contacted police on August 8 about one passport which gave us cause for concern, for example.

“The owner no longer works for us so we cannot comment further on this case.”