Miss Brand, who also serves with Norfolk police, was left terrified by Curtis's "possessive and controlling behaviour", which included him attacking her, kicking her dog and even threatening to throw himself out of a moving car and under a lorry.

Lincoln Crown Court heard the couple started going out in 2005 after meeting at the Terrington Beat Base in Terrington St John, Norfolk, where they were based.

Michael Cranmer-Brown, prosecuting, said Curtis, who had recently left his wife and was on medication for depression following a car crash, turned out to be "volatile and somewhat unstable".

He said: "When his medication was combined with drinking his character changed and he was something of a Jekyll and Hyde."

He said incidents included Curtis threatening to throw himself out of a car they and friends were in on the way back from the seaside, taunting her that he had had sex with his former wife, and smashing a glass over his own head, claiming he would then have her arrested for assault.

The court heard one terrifying episode came in August 2006 when he pulled the handbrake as WPC Brand drove at 60 mph. Later that night she woke to discover the house full of fumes after Curtis had turned on a petrol-driven motor in the utility room.

Mr Cranmer-Brown added: "She was terrified. She was extremely frightened about what he would do next. She went to bed shaking like a leaf.

"He was lying next to her. He pulled the duvet above her mouth and nose. She was anxious about whether he was going to smother her."

After the relationship ended he bombarded her with text messages before finally saying he had moved his belongings out of her house.

But when she returned home she found her house in a state of disarray.

Mr Cranmer-Brown said: "Her vibrator had been broken. You may think he picked on that because he thought she might be too embarrassed to complain."

Curtis denies charges of harassing WPC Brand, attempting to administer a noxious substance to her and causing a danger to road users.