**GRAPHIC WARNING: Images below contain scenes of a sexual nature**

(Image: DS )

The randy duo were filmed getting down and dirty on the 8.40pm Northern service last Bank Holiday Monday.

Now train bosses are probing the footage, which is too explicit for Daily Star Online to publish.

In it, a woman with her trousers pulled down is sitting on her male partner’s lap.

She then begins performing a sex act on him in full view of horrified passengers, including young kids.

(Image: DS )

(Image: DS )

One witness, who gave his name as Olly, said he started filming the shocking scene on the journey back from visiting his girlfriend.

He told Daily Star Online: “It was a very busy service with kids on there.

“There was a lady sitting behind them and a couple in front of them and they both moved away.

“To be honest, they seemed drunk or drugged up – they were really loud when they got on board and people were moving away from them.”

And shockingly, Olly claims that despite reporting the bonk-mad couple to the conductor, they were allowed to continue on their journey to Manchester.

He added: “They were at it for at least 20 minutes – I felt sick.

“It’s just such a shocking thing to do in full view of people on a train.”

Northern has said it is investigating the incident.

A spokesman told Daily Star Online: “Northern is committed to providing a safe and secure environment for all of our customers.

“We take a zero-tolerance approach to any type of anti-social behaviour.

“This incident is under investigation and we will ensure the appropriate action will be taken.”

Daily Star Online has contacted British Transport Police over the video.