A City banker who bludgeoned a woman to death with a pestle on her 29th birthday has been jailed for at least 19 years.

Zahid Naseem struck Christina Abbotts, a sex worker, 13 times on the back of the head with the ceramic kitchen utensil in May.

The 48-year-old financial consultant claimed he hit her in self-defence, fearing he was being strangled to death in a sex game gone wrong. But a jury at Lewes crown court found him guilty of murder after four hours of deliberations.

Abbotts, who was born in the West Midlands, was described in court as a “socialite” who led a party lifestyle in London. Her family believed she worked in IT but she had secretly advertised her services on the AdultWork.com website under the pseudonym Tilly Pexton.

Naseem was working for Toronto-Dominion bank’s London office when he found her profile offering overnight rates of £1,000.

The pair were last seen in public on the evening of 24 May when Naseem met her in Crawley, West Sussex before they spent the night together. CCTV showed him standing in an Asda supermarket aisle kissing her on the forehead as they bought her favourite brand of champagne, Veuve Clicquot.

Christina Abbotts was described as a ‘loving, caring’ daughter. Photograph: Rex/Shutterstock

Worried friends started searching for her when she failed to turn up to her birthday party in South Kensington the next day.

Police found her body when they broke down the door of a flat in Crawley in the early hours of 26 May. They discovered Naseem pretending to be unconscious in the next room.

The freelance risk management consultant, who earned up to £250,000 a year and had previously worked for the investment bank Merrill Lynch, initially claimed he could not remember the incident when police interviewed him.

When he gave evidence in court, he admitted striking Abbotts but claimed it was in self-defence. He also said a “red mist” may have come over him. But the prosecutor, Christopher Tehrani, dismissed his testimony as a “pack of lies”.

Abbotts’ parents paid tribute to their “loving, caring” daughter and said the picture painted of her in court did not fully reflect who she was. “It has not been mentioned but we would like to clarify that Christina held many legitimate jobs in estate agency and events,” they said in a statement on Thursday.

“She is not here to defend herself in this case and the way she has been portrayed does not reflect and define our Christina. What has been highlighted in this case does not change the fact that she was a loving, caring and loyal daughter, sister, niece and friend.”

The judge, Christine Laing, said Naseem’s attack on Abbotts was of “extraordinary ferocity”. “When I consider the extent of all the injuries, you inflicted considerable pain,” she said. “The terror of her final few moments of life is unimaginable.”

Laing said Abbotts, as an escort, “had chosen to earn her money in a business that is as old as time. And one that has always carried with it huge risks of danger, as this case sadly demonstrated.”