A serial sex offender who stared at a teenage girl while masturbating on a Sutton bus has been jailed for four months.

Morden man James Gathercole, who acts as a carer for his disabled mother, followed the 17-year-old girl to the back of the 151 bus where he stared at her while masturbating for 10 to 15 minutes on August 21.

The 28-year-old was arrested after the girl took a covert picture of him and sent it to the Sutton Guardian. Initially the Blanchland Road man told police he could not remember what he was doing but, after seeing the picture, admitted the offence and claimed stress from the death of his father caused him to do it. He pleaded guilty to exposure last month.

Your Local Guardian:

James Gathercole at Croydon Magistrates Court for an earlier hearing

Despite his defence calling for leniency on the grounds he is the sole carer for his disabled mum, Gathercole was jailed as his girlfriend looked on from Croydon Magistrates' Court's public gallery. As he was led to the cells following the hearing on Friday he called to his girlfriend, saying "take care of mum, yeah".

The court heard how the Sutton teen got onto the upper deck of the 151 bus near Rosehill at around 4pm. As a seat near the back of the bus became free, she moved into it but noticed Gathercole had followed her. Prosecutor Sam Main told the court: "She was minding her own business with her earphones in when she noticed in the reflection on the window that James Gathercole had exposed his erect penis and was masturbating.

"Under the pretext of making a phone call, she managed to take a picture. It carried on for 10 to 15 minutes until she left the bus. When she left the bus Gathercole desisted.

"The matter was reported to police, there was some publicity including the complainant posting the picture on twitter and a report in the newspaper. He was identified because of that publicity.

"Initially in an interview he provided an account saying he couldn't remember what he'd done. He said he does get that bus but he didn't expose himself.

"He was shown the photograph and further interviewed and he accepted is was him. and gave an explanation -  the reason was because his father had died and he's the sole carer for his mother who has mental health issues.

"That doesn't explain similar matters in his previous convictions."

The court heard Mr Gathercole has five previous convictions for sex offences, all indecent exposures, dating back to 2004 and was sent on a sex offenders' course as a result.

David Allman, defending, told the magistrates that if they sent Gathercole to prison it would mean his mum would have to go into a home but the panel decided a custodial sentence was necessary.

Magistrate Mr Fisher said: "This was an offence on a 17-year-old victim on public transport and, to some extent, you targeted her.

"You had an intervention before and that hasn't worked. You were given your opportunity and you didn't take it."

Gathercole has  also been placed on the sex offenders register and must notify police of his address for the next seven years.