A SENIOR policeman who had an affair with a top City lawyer's wife yesterday denied setting up the husband to take the blame for an arson attack that destroyed his car.

Chief Supt Jim Trotman, 45, was at Swindon Crown Court yesterday accused of allowing Ian Gray to be the "fall guy" for the blaze that wrecked his Citroen Picasso.

The Thames Valley Police officer was in a secret 20-month affair with Mr Gray's wife, Karin, when his car was torched in an arson attack on the night of October 20, 2009.

The prosecution alleges that father-of-two Trotman doused the car in petrol and set fire to it after parking it close to his lover's home in Bedwells Heath, Boars Hill, near Oxford.

The former Marine is also accused of attempting to pervert the course of justice by allowing Mr Gray, who works in London-based law firm Eversheds, to take the blame.

During a second day of cross-examination at Swindon Crown Court, prosecutor Fiona Elder asked Trotman: "Did you set up Mr Gray to be the fall guy for the arson?"

Denying the accusation, Trotman replied: "I have no reason to set him up.

Their marriage was over. It was not in my interest to harm Mr Gray.

"I was not setting him up in any way at all."

Hours before Trotman's car was set alight he had spoken to a senior colleague about several threatening emails he had received reporting to show that Mr Gray knew of the affair and had hired a private investigator.

"Did you know when you spoke to Det Supt Ashley Smith earlier that afternoon that you were going to set fire to your car?," Miss Elder asked.

"As I have said on a number of occasions in this witness box I did not set fire to the car. I don't know who did and I am not connected with that,"

Trotman replied.

Mr Gray was arrested at his home on the evening of October 21 on suspicion of conspiracy to commit arson.

Trotman, who at the time was estranged from his wife Charlotte, said he and Mrs Gray had been taken to a police station that night and told of Mr Gray's impending arrest.

However, from the witness box he denied knowing for what charge and said he believed it was related to domestic violence because the officers questioning Mrs Gray, he knew to be specialised in domestic violence.

"The whole aura was domestic violence," he told jurors.

"My assumption was that he was going to be arrested for domestic violence."

Miss Elder asked the defendant to explain his comment and he replied: "Mr Ian Gray was a controlling individual. He used financial control over his wife.

"I was not investigating this and I knew Mrs Karin Gray was receiving a very good service from the domestic violence assessment."

Miss Elder asked: "You knew Mr Gray was being arrested for arson and you had sown the seeds for that the previous day?"

Trotman replied: "No, I disagree with that."

When suspicion began to fall on Trotman the following month, police began recording calls he made from his office telephone.

In one recorded call with Det Supt Smith, Trotman agreed that he suggested Mr Gray might be responsible for sending the emails.

Miss Elder read extracts from the transcript of the conversation to the court.

Trotman had told Det Supt Smith: "Mr Gray is a lawyer and he is not likely to incriminate himself."

Miss Elder asked him: "You accept that he might still be responsible for the emails and you are suggesting within this phone call that Ian Gray was responsible for the arson?"

Trotman denied the assertion that he was trying to blame Mr Gray for the fire and added: "He had intervened in the previous affair back in 2001.

If I were leading the investigation I would want to know who he got to hack into his wife's email.

"Ian Gray was under arrest for a serious offence and Ian Gray should have been asked that question in my professional opinion."

The court has heard how Trotman had arranged to spend the evening with Mrs Gray while her husband was away on business.

The officer said that in a statement to police on the night of the fire he said he had arrived at Mrs Gray's home at 9.45pm having watched his daughter perform in the Railway Children at a local theatre.

However, Trotman accepted that following the mobile phone evidence presented to the court he would have arrived later, placing him in the vicinity when the Citroen was set alight shortly before 10.30pm.

Miss Elder asked: "If you arrived at 9.45pm you are a long way away from when the car was set alight? A fire that you didn't think would be investigated thoroughly?"

Trotman denied the accusation and said: "No, I would have thought that a chief superintendent's car being torched would have received a significantly different level of service."

Neighbours alerted the police and fire brigade having seen the car on fire at 10.30pm but did not hear the smashing of a window or a car alarm.

An agitated Trotman returned to the smouldering wreckage at 11.30pm.

The prosecution allege that the police officer told two firemen: "That's my bloody car. I've been seeing someone I shouldn't have been seeing but keep that between me and your crewmate."

Miss Elder asked the defendant: "Are you at the scene suggesting that Mr Gray, although you may not have named him, is responsible for the fire to your car?"

Trotman replied: "No I am not."

He went on to explain that he did not tell his lover of the fire that night because he did not want to worry her and wanted her to get a good night's sleep.

Miss Elder asked Trotman whether he had any concerns for Mrs Gray's personal safety given the fire and the threatening emails.

"At that stage I am not exactly sure what's going on. I have never believed that Mrs Karin Gray was under threat from Mr Ian Gray," Trotman said.

"It is still incredible to me that Ian Gray would do anything to harm Mrs Karin Gray or her children."

The police officer denied Miss Elder's assertion that the reason he did not tell Mrs Gray about the fire was because he had no reason to be concerned for her safety, as he had started the blaze.

After the arson, Elephant Insurance paid out GBP14,820 and The Warranty Group - who Trotman had a policy insuring against the loss of the value of the car - paid GBP4,880.

He then used the insurance money to buy an Audi A4 convertible, the court heard.

Trotman joined Thames Valley Police in 1992 having previously served in the Royal Marines, where he saw active service in Northern Ireland and Iraq.

At the time of his arrest he was head of the force's strategic development department and was the former police commander for Oxford.

Trotman, of West Quay, Abingdon, Oxfordshire, denies arson, attempting to pervert the course of justice and two counts of fraud by false representation.

The trial continues.