Two former detective constables have been jailed for sabotaging child abuse investigations out of laziness and “cynical disdain” for vulnerable victims.

Sharon Patterson, 49, and Lee Pollard, 47, forged documents, concealed evidence and lied about investigations. The pair were sentenced to 18 months and two years in prison respectively.

The Old Bailey was told Patterson ditched work to go for a manicure and have a four-hour lunch at a Chinese restaurant with Pollard, who was married and with whom she was having an affair. After forging a document to close an investigation, he described her in a flirtatious email as his “deceptive partner in crime”.

The pair, who now live together in Colchester, Essex, denied wrongdoing, citing administrative chaos at the child abuse unit in north Essex at which they worked.

The judge, Nigel Lickley QC, told them they had shown “contempt” for victims when they chose to shut down investigations rather than put in the work, believing they would never be found out.

“People relied on you to do your job to the standard expected. You abused that position for your own selfish purposes,” he said. He added that if pressure at work had been a factor, the couple should have sought help.

In March, Pollard was found guilty of two charges of misconduct in public office and Patterson was convicted of one similar offence.

Earlier, Alexandra Healy QC, prosecuting, said the officers’ “deliberate and dishonest conduct” had caused harm to the public of the “utmost seriousness”. She highlighted one complainant, who took years to gain the courage to come forward and had felt it was “really important it was dealt with properly”.

Mitigating, Jacqueline Carey told the court that Patterson had “soldiered on” in a child abuse unit “in crisis” and “crippled by the loss of staff”. Craig Rush, for Pollard, said he had not set out to act as “judge and jury” in his misguided attempts to “separate the wheat from the chaff”.

He added: “It was not a failing police department; it was a failed police department. In a world where public expenditure is pared to the bone, there are consequences, and one of those consequences was that this police department had, by 2013, failed.”

The corruption investigation into offences between 2011 and 2014 has been under way for the past four years, with the misconduct coming to light in 2014 after a victim complained her signature had been forged – and misspelled – on a statement taken by Patterson.

The investigation into the Essex police unit, which involved looking into 30 officers, was undertaken by Norfolk police and the police watchdog.

A total of 296 Essex child abuse cases were looked at, of which 55 were referred to the Independent Office for Police Conduct. Patterson and Pollard were the only officers to face criminal charges, although a third officer was sacked for gross misconduct last year.

Pollard had destroyed four indecent photos of a complainant in another case while it was still being investigated, the court heard.

He also did not investigate an allegation of sexual touching by a teenager, then lied by claiming no further action was to be taken on the advice of the Crown Prosecution Service. Pollard was dismissed for gross misconduct in September 2015.

Following her conviction at the Old Bailey, Patterson was also sacked and both now risk losing their police pensions.

The allegations against the officers came to light when performance reviews were carried out into the child abuse investigation team in which they worked.