A 17-year-old boy who harassed a same-sex couple on a night bus did so because he believed they were lesbians, a judge has ruled.

Melania Geymonat and Christine Hannigan were attacked shortly after 2.15am by a group of teenagers on May 30 while on a date.

CCTV of the incident showed the pair were surrounded, hit with coins, punched and subjected to sexual gestures while travelling on the top deck of the N31 bus in West Hampstead.

On Thursday, three teenage boys - aged 15, 16 and 17 - admitted using threatening or abusive words or behaviour to cause harassment, alarm or distress against the two women shortly before trial.

Although the 17-year-old denied he was hostile towards the women based on their sexual orientations. District Judge Susan Williams disagreed, finding that his role in the incident was motivated by hostility towards their sexuality.

The teenager, who did not speak to the couple at any point, approached the women later than his co-defendants.

After laughing and joking with the other teenagers, he was handed coins by the 15-year-old, who made a sexual scissoring gesture towards the women.

The 17-year-old was later involved in a scuffle with Ms Hannigan and others at the back of the bus, the judge found.

Appearing at Highbury Corner Youth Court on Friday, the teenager said he approached the women later than the rest of the group did because the conversation seemed "friendly".

The 17-year-old told the court Ms Hannigan was crouched at the front of the bus pretending to vomit in an attempt to get the group to leave her and Ms Geymonat alone.

Giving evidence herself, Ms Hannigan said they were physically cornered by the teenagers and were "harassed because of who we were".

She said: "We were clearly together in a romantic sense, we were being affectionate.

"It is pretty intimidating being cornered and making homophobic comments."

She added: "You feel embarrassed being targeted for your sexual orientation."

Passing judgement, the judge said: "I am quite sure this was a hostile act however I also have to be sure that you were hostile because Ms Hannigan was a lesbian.

"In other words that you were picking on her because of who she was and not just fooling around.

"I have come to the short conclusion that is exactly what you were doing."

She added: "Those two ladies were being harassed, pestered and intimidated because of who they were.

"I am quite sure you were joining in that behaviour."

The 17-year-old was sentenced to a four-month youth rehabilitation order and is barred from contacting his co-defendants over the same period.

He will also face 20 hour reparation requirement, similar to community service, and a two week curfew.

Judge Williams also suggested he write a letter of apology to the two women.

Two 15 and 16-year-olds who did not contest the prosecution's case will be sentenced next month.

Additional reporting by PA.