A London Underground worker who discovered the mother of his children had been exchanging raunchy photos with another man went berserk and trashed her house.

Karl Johnson sent his ex a text which read “I swear to God I will kill you and him” before causing damage worth more than £2,000 to her Canterbury home.

The 30-year-old told city magistrates that he “lost it” after his former girlfriend told him she had been having phone sex and sending photographs to another man.

Prosecutor Adrian Crossley described the events of the early morning of June 13 as a “prolonged, extremely nasty incident”.

He said Johnson, who lives in Austin Avenue, Herne Bay, had been asked to look after two of his three children after the third was taken to hospital with breathing difficulties.

"A witness who lives nearby rang police to report that the defendant was smashing up vehicles and cutting their tyres with a knife" - Prosecutor Adrian Crossley

Johnson, who had been in a relationship with the woman for a decade until they split up, had gone to her home near the Christ Church campus at 11.30pm.

At 4.06am, Johnson sent her the message in which he threatened to kill her and the other man. Mr Crossley told the court that the message also contained swear words.

He added: “At 4.24am, a witness who lives nearby rang police to report that the defendant was smashing up vehicles and cutting their tyres with a knife.

“He was seen discarding a knife and police were called. They later realised that the threatening message, which the victim had reported, and this incident were related.”

Police went into her house and found damage to a cooker, a rug, a glass vivarium, a mirror, a table, four chairs, two glass lampshades and a toy car.

Johnson had also damaged his ex's blue Seat Ibiza, as well as a red Vauxhall van which was also parked in St Gregory’s Road.

Mr Crossley said the damage to the vehicles and to the property inside the house was estimated at £2,255. Johnson handed himself into police at 10.30am that day.

In court he admitted criminal damage and sending a message which was grossly offensive, indecent, obscene or menacing.

Johnson told magistrates that he was on his way to a night shift for London Underground when he got the call that one of his children was being taken to hospital.

He said the other two children had been collected by another family member and were not in the house when the damage was caused.

“She had told me that she was seeing someone else and said she had been having phone sex, sending photographs,” Johnson said.

“I just lost it. I haven’t got a good reason for it and I don’t think it’s right. It just happened.”

Johnson was released on bail and will be sentenced on August 24. Magistrates told him they had not ruled out sending him to prison.