A paedophile found with indecent child images as his phone wallpaper has been jailed after a shocked passenger spotted him watching abuse videos on a train. 

David Johnson, 35, was caught viewing videos of young children being abused while on a train from Stafford to London on September 23.

The sex offender had moments earlier been spotted messaging a contact asking: 'What kinds of videos do you like? I have all kinds.'

He soon received a reply which read: 'Just kids videos.' 

A passenger sitting behind Johnson witnessed the disturbing exchange and the videos that followed and alerted British Transport Police after moving to another carriage.

Officers swooped to meet the train as it arrived at London Euston station and arrested Johnson on suspicion of possessing indecent images of children.

He was initially released on bail before being charged in December, and this month was sentenced at Inner London Crown Court to two years and three months behind bars.

During his arrest, officers searched the paedophile and seized his phone - which was found to have an indecent image of a child saved as the wallpaper.

While in custody, Johnson even asked officers if he could have his phone back because he 'needed to delete some stuff'.

Further analysis uncovered nearly 200 indecent images, including 105 Category A pictures, the most serious.

Officers also found messages where Johnson believed he was speaking to a 13-year-old girl and had arranged to meet her for sex. It was later confirmed the child did not exist.

Johnson offered no comment during police interviews.

Devices were also seized from two addresses linked to him.

He pleaded guilty to six counts of making indecent images of children, two counts of attempting to engage in sexual communication with a child and arranging or facilitating a child sex offence.

On top of his prison sentence, Johnson was also handed a 10-year Sexual Harm Prevention Order and will remain on the sex offenders' register for a decade.

Detective Constable Victoria Lowth said: 'The quick thinking and courage of the man who saw Johnson's phone meant that we were able to quickly arrest him and uncover the scale of his offending.

'I'd like to offer our sincerest thanks to that man, whose actions have directly led to Johnson's imprisonment.

'Behind every image and video Johnson owned is a vulnerable child that has been exploited and abused.

'He is clearly a danger to children and has rightly been handed substantial jail sentence, and stringent conditions have been put in place to prevent him from offending further.

'We will always do everything we can to make the railway a hostile place for criminals, and especially those whose offending targets children.'