An Essex police officer sexually assaulted a woman in a bar while he was on a night out with other officers, it has been alleged.

Stuart Chaplin was captured on CCTV in the smoking area of the Walkabout Bar in Chelmsford smacking the woman's bottom as she bent down to the floor to get a lighter out of her handbag, Ipswich Crown Court was told.

The woman turned round and allegedly saw Chaplin, who was at a colleague's leaving-do with a group of other police officers, "laughing and smirking", said Gareth Hughes, prosecuting.

Later the same evening the woman was getting ready to leave the bar when Chaplin had allegedly grabbed the base of her bottom and squeezed hard.

"He didn't make contact with the area of her vagina but it was very close," said Mr Hughes.

"She pushed him as hard as she could," Mr Hughes told the court, saying the woman told Chaplin to leave her alone in no uncertain terms.

Mr Hughes said the woman hadn't invtied Chaplin to touch her or flirted with him during the course of the evening.

Chaplin, 25, who lives in Witham, has pleaded not guilty to two offences of sexual assault and one of exposure on May 26 last year.

After the incident came to the attention of the police, Chaplin was interviewed by officers in July last year and denied sexually assaulting the woman by slapping her bottom in the smoking area and squeezing her bottom in the bar, said Mr Hughes.

Chaplin told officers that during the evening his trousers had ripped and he had called his mother to bring him another pair of trousers after he was told he couldn't stay in the bar dressed like that.

Mr Hughes said the first alleged assault on the woman was captured on CCTV which also allegedly showed Chaplin exposing himself.

When Chaplin was interviewed by police again in August he accepted hitting the woman on the bottom but claimed she had been flirting with him all night and he had done it "jokingly".

When asked about exposing himself he allegedly said he didn't know why he had pulled his trousers down.

The trial continues.