An Ilford man has described the moment he saw a sexual deviant touching himself on a packed Tube in rush hour, which helped police catch the pervert.

Repeat offender Justin McCarthy, 37, of no fixed abode, was jailed for 21 months on Tuesday at Blackfriars Crown Court for a string of public indecency offenses across the underground network.

McCarthy would board the Tube, sit near a woman, and begin to touch himself under his clothing.

He would stare at the woman and attempt to gain her attention by tapping his feet.

A 38-year-old man from Ilford’s testimony and photographs helped identify McCarthy and link him to crimes, which he has now been prosecuted for.

The witness was on the Central line near Wanstead on his way home from work, on August 8 last year, when he encountered the pervert.

“I managed to get a seat opposite a woman on a busy carriage with a mix of commuters and tourists,” he told the court.

“Somewhere between Leyton and Wanstead, something drew my attention to the young man sat next to the woman.”

“He was slouched back with his legs spread and I noticed that he had one hand inside the waistband of his jeans and was masturbating.

“At first I doubted what I was seeing, but then the man leaned over towards the woman and began whispering into her ear.”

The man said the woman looked “horrified” so he offered her his seat, and stood between McCarthy and the victim.

He continued: “There were other women and children on the train and I tried to position myself so that I obstructed his view as much as possible.

“I couldn’t believe this was happening and it was a very unpleasant to watch.”

The man then bravely took a photo of McCarthy, and followed him after he got off the Tube at Newbury Park.

He immediately reported the incident to the British Transport Police, and the photo helped identify McCarthy.

McCarthy was jailed for six offences between February and March in Brent Cross, Oxford Circus, Watford Junction, Morden, Clapham South and Waterloo Tube stations.

Siwan Hayward, Transport for London’s head of transport policing, said: “The actions of McCarthy were demeaning, unacceptable and intimidating.

“We do not tolerate unwanted sexual behaviour on London’s public transport and I commend all those who came forward to report what they saw.

“Every report matters and it helped police build a picture so they could catch McCarthy and sentence him for his offensive, disgusting crimes.”