BORIS Johnson grimaced and exclaimed "you are joking" as he was shown a body scan from a prisoner who had tried to smuggle contraband into jail in a Kinder egg hidden inside his body.

The Prime Minister toured HM Prison Leeds, an inner-city Victorian jail, where staff told him the introduction of a state-of-the-art scanner had led to a reduction in drug smuggling and therefore violence.

Mr Johnson spent around 90 minutes touring the prison, where he talked to managers, guards and inmates.

He was given a demonstration of an £80,000 torso and body scanner which is used on new inmates, recalled prisoners and those who have been to court, and which uses sophisticated X-ray imaging to detect contraband.

Since it was introduced in December, 4,500 scans have been undertaken and around 60 seizures of drugs, tobacco or mobile phones made.

Mr Johnson, who announced an extra £100 million for airport-style security in prisons in England and Wales, was shown a stored image of a body scan which showed a Kinder egg secreted inside a prisoner. It was later found to contain tobacco. He exclaimed: "You are joking."

Tobacco has been a contraband item since smoking in jail was banned.

Another stored image on the scanner clearly showed one mobile phone in an inmate's stomach that he had swallowed, plus another two in his bowel.

Mr Johnson walked through the prison before meeting senior management and joked he had been shouted at on his way through, claiming it was a supporter.

The PM insisted that state agencies needed to "wrap their arms around" problem families to prevent young people getting sucked into crime.

After announcing a raft of law and order spending commitments in the last few days, including increasing the number of police officers by 20,000 and prison places by 10,000 south of the border, he said: "I don't want to see prisons just be factories to turn bad people worse. We need to be making sure that they are educated and there's not a culture of gangsterism and drugs in the prison system."

Mr Johnson walked through the prison rotunda, up spiral stairs and into a meeting room where he shared a cup of tea with prison warders, then walked down A-wing to meet one of the jail's 1,100 inmates.

No details were given about the identity of the prisoner or what offence he had committed.

A-wing was for inmates who had volunteered to take part in a drug treatment programme.

One sign on the wall of the prison stated "HMP Leeds, protecting the public since 1847" and the most recent inspection two years ago stated that the local Category B jail with 667 cells was one of the country's most overcrowded.

In the 2017 inspection, 60 per cent of prisoners reported that drugs were easy to obtain.

Following the visit, Mr Johnson confirmed the Government would spend £100m on X-ray scanners and metal detectors "to protect the staff and to stop the prisoners bringing in, to put it bluntly, in their alimentary systems, drugs and mobile phones, which greatly degrade the life in prisons".