Former Chief Inspector Rob Leet also met a woman for sex while on duty who he knew was a victim of domestic violence, a hearing was told this week.
Assistant Chief Constable Nick May condemned Mr Leet and said his actions were a ‘fundamental betrayal’ of the public.
Leet was serving as district commander for Lewes and Wealden during the time of his affair with PS Sarah Porter.
Ms Porter was previously a sergeant on the Rother Neighbourhood Policing Team but had been based at the roads policing unit in Polegate up until today.
Ms Porter was dismissed without notice. Mr Leet resigned from Sussex Police prior to the hearing but as a result of the panel ruling will be placed on a barred list.
Pair denied their relationship was sexual
Mr Leet and Ms Porter had denied that their relationship was sexual but a panel today found they had breached professional standards of behaviour, the Independent Office for Police Conduct (IOPC) announced.
Investigators revealed how the pair would travel to meet during work when there was no work-related purpose, and repeatedly used Sussex Police communications systems to exchange messages where there was no work purpose.
Officers 'ignored their duties to their community for their own personal gratification'
IOPC regional director Sarah Green said: “These two officers ignored their duties to their community and their colleagues to pursue a relationship for their own personal gratification during working hours.
“Our investigation found that this even led to PS Porter failing to be available to attend a fatal crash while she was on call.
“Ch Insp Leet was also in a relationship with a woman who he knew was a victim of domestic violence who he met for sex while he was on duty.
“The inappropriate behaviour of these two officers has brought Sussex Police into disrepute and I hope the decision of the panel to dismiss the officers will send a clear message that this behaviour will not be tolerated.”
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Pair found guilty of gross misconduct
As reported by the IOPC, the panel ruled that the pair did engage in sexual activity while on duty and this constituted gross misconduct. The panel ruled the misuse of police communications systems was misconduct.
The panel also found that Ch Insp Leet engaged in an inappropriate sexual relationship with Mrs A and met her to have sex while on duty and this was gross misconduct.
The panel ruled that PS Porter’s failure to be available to respond to a fatal road traffic collision was misconduct.
Senior Sussex Police officer condemns their actions
ACC Nick May said: “We expect the highest possible standards of our officers and staff and we take any report of inappropriate behaviour extremely seriously. The behaviour of both of these officers is a violation of the trust that the public put in the police to serve and protect them. They have let down the people of Sussex and their colleagues.
“Rob Leet has also let down a vulnerable woman who looked to him for reassurance and support. He chose to resign shortly before the hearing. When police officers or staff abuse their position of trust for a sexual purpose, particularly in respect of vulnerable people, such behaviour represents a fundamental betrayal of the public and the values for which the police service stands.
“We have a responsibility to recognise abuse of power as a distinct area of corruption, behaviour which deflects from the work of the vast majority of officers. Vulnerable victims must be able to trust those they turn to for help.
“We have adopted and implemented the National Police Chiefs' Council’s national strategy to address the issues of police officers and staff who abuse their position for a sexual purpose or to pursue an improper emotional relationship. We are ensuring that all staff are aware of appropriate professional boundaries and the serious consequences of any abuses of position.”