A Royal Navy lieutenant has been jailed after he started an affair with a 15-year-old girl which he carried on even after he had been caught with her in a hotel.

David Anderson, aged 44, met the schoolgirl through an internet dating site where she claimed she was 18 but later discovered her true age.

He continued seeing her and having sex after his arrest and put so much pressure on her to withdraw her police statement that she tried to commit suicide.

Anderson is a former Royal Marine marksman who switched to the Royal Navy and has saved many lives while working as an observer on a Search and Rescue Helicopter at RNAS Culdrose in Cornwall.

He is an Iron Man endurance runner who has raised £45,000 for Royal Marine welfare charities. During his 27 year career he trained with the Marines at Lympstone and served with 40 Commando at Taunton, 42 Commando in Plymouth, and 45 Commando in Arbroath.

He was happily married with two children but started the affair after suffering a breakdown caused by post traumatic stress disorder induced by horrors he witnessed in Northern Ireland and Afghanistan.

He has already been told he is being discharged from the Navy because of his medical condition, which has been confirmed by a consultant psychiatrist.

Anderson, from Falmouth, admitted two offences of sexual activity with a child and attempting to pervert the course of justice and was jailed for two and a half years by Judge Simon Carr at Exeter Crown Court.

He told him:”You have an exemplary service record and have served your country at home and abroad and regularly put yourself in personal danger. It would be difficult to imagine a more impressive record.

“It is also perfectly clear at the time you were suffering from PTSD as a result of what you had seen and done.

“However, last year you were in your 40s and with a family and chose to go onto a dating site you identified your victim who told you she was 18. Even a moment's reflection on the age gap should have raised concerns this relationship was inappropriate.

“She was clearly vulnerable. There is evidence of self harm and significant attempts on her life. Her parents were concerned and went to the police.

“Whatever the position before that, after your arrest you could have been under no possible illusions that she was a child. It should have been a sharp wake up call.

“You were also under bail conditions not to contact her. These offences took place when you were aware of the concerns about her. You met her even though you knew she was a child and there was full intercourse.

“She was vulnerable but you brought emotional pressure on her, indicating the effect on you and your family to try to convince her to withdraw her statement and make a complaint against the police.

“The fact that these offences happened after your initial arrest when you knew you must have nothing more to do with the girl mean that a custodial sentence is inevitable.”

Miss Julia Cox, prosecuting, said Anderson met the girl last year after seeing her on the internet dating website Luvoo where she lied about her age and said she was 18 and he lied about being married.

They met and had sex but he was arrested when he was with her at a hotel in West Cornwall in July after her parents reported her missing.

She told police about their three previous meetings and he was bailed on condition he had no further contact with her but went on to see her and have sex again when he was aware she was only 15.

They kept in contact through Snapchat and on a 'clean' SIM card which she put into her phone when she rang or texted him. One of his texts suggested they may eventually get married.

He urged her to withdraw her statement and make a complaint against the police handling the case and his contact with her only came to light when she took an overdose and was taken to hospital.

Miss Cox said: "She said she had felt sorry for him and he told her he was missing her. He told her he was worried about the case getting in the papers and the breakdown of his family. She described feeling awful about what was happening.

“She went to his home address on a couple of occasions and once he messaged her indicating he was outside her home as she was on her way to school.”

Mr Peter Glenser, defending, urged the Judge to pass a suspended sentence so Anderson could receive the specialist treatment he needs for PTSD and emotionally unstable personality disorder.

He said Anderson had a flawless military record, having joined the Royal Marines when he was 17 and served in Northern Ireland, Iraq and Afghanistan leading to traumatic experiences which have had a deep effect on him.

He left the Corps in 2007 and was commissioned as a Lieutenant in the Royal Navy and served as SeaKing rescue helicopter crew, taking part in many rescues around the South West since 2009 but being further traumatised by recovering bodies from maritime tragedies.

He said he had been recommended for an honour for his military service and charity work but had been arrested before it was awarded. He was also a marksman who won the Queen's Medal at Bisley three times and represented his country.

He said:”He is very far from an emotional predator. He is a man who has put his life on the line for others day in and day out. It is easy to overlook the powerful sense of shame he feels now, not just for himself but for the Corps, the Royal Navy and his family.

“Some might see this man as a paedophile. He is not a paedophile. He is not sexually attracted to children or a danger to children. He fell in love with someone who told him she was 18.”