A 53-year-old Leytonstone man was found guilty of sexual assault after an undercover police sting on the Tube.

Muhammed Tahir rubbed himself up against a young female commuter during the rush hour on London Underground.

He followed the "confident and articulate" woman on to a Central Line train after watching her on the platform.

Tahir came alongside the woman and pretended to accidentally slide his hand across her thigh as she stood with other commuters in the crowded carriage.

When the 20-year-old attempted to move, he sidled even closer and started rubbing his potbelly and crotch against her bottom.

His behaviour attracted the attention of undercover police officers who were watching his every move.

The distraught woman managed to alert the attention of undercover police officers and Tahir was arrested.

Police later found out that he was charged with two previous, similar offences in 2003, but managed to be cleared only after the prosecution file failed to get to the court on time.

At the Old Bailey, Judge Rebecca Poulet QC said that the experience was clearly very "frightening and shocking" for the victim.

The judge told Tahir: "Your purpose in getting off was not because you were hot as you claimed but in order to look for a suitable young woman and to follow her on to the train for your activities.

"That is exactly what you did. So blatant was your conduct that no less than three undercover police officers saw you doing it and saw you looking at young women.

"You spotted [the victim] and followed her on to the Central Line train. It was fairly crowded and she stood centrally in the area near the double doors holding the rail with her right hand.

"When the train moved off she felt something brush her left side. She looked down and saw your hand by her side in a somewhat unnatural position and it made her uncomfortable.

"She moved to get away from you, still thinking the touching might be accidental. When the train moved again you came closer, pushing your stomach up against her and then your crotch.

"She leaned as far as she could in order to move herself away from you but you moved with her, pressing up against her. You pressed your crotch on her thigh and buttock. She could feel you pressed firmly against her buttock.

"Despite being a confident and articulate and fair witness she cried giving evidence and the experience was clearly frightening and shocking for her.

"In my view there must be a custodial sentence. You were in grave peril of going immediately to prison. I want to impose a sentence that will prevent you from behaving like this ever again and the public is best served by suspending this sentence."

Poulet ruled out a prison sentence for the dry cleaner, enforcing the five-year ban on London Underground, while also being under the supervision of probation officers.

According to the British Transport Police (BTP) 90% of sexual harassment goes unreported.

The Report It To Stop It campaign created by the BTP encourages women to inform police of such behaviour and has already seen a 30% increase in both reporting of sexual offences and suspects caught.