Two police officers have been brought before a disciplinary panel accused of running an unauthorised surveillance operation against a woman whose brother was unlawfully killed in a police station.

The pair, who have been granted anonymity, could be dismissed if they are found guilty of gross misconduct at the disciplinary hearing, which opened on Monday.

Janet Alder has described how she felt “terrorised by the state” during her campaign to discover the circumstances in which Christopher Alder, a former paratrooper, died at a Hull police station in 1998.

The panel, which is scheduled to sit for five days, was told police followed her and her lawyer at his inquest on 28 July 2000 and attempted to listen to conversations between them.

Such exchanges are private and confidential under legal rules that protect conversations between lawyers and their clients.

The panel of three heard the surveillance team followed Janet Alder and her barrister Leslie Thomas to a hotel and car park. As many as 14 officers took part in the operation.

Dijen Basu, the QC for Humberside police, described the surveillance as intrusive and said it lasted nearly two hours “without appropriate authorisation and justification”.

The operations commander and deputy operations commander are alleged to have conducted surveillance that went “far beyond the strictly limited terms” of what had been authorised. Both deny gross misconduct.

Jason Pitter, the QC for one of the officers, said they had acted on instructions. “The culpability lies with others further up the chain. The spotlight should not be on this officer,” he said.

Sam Green, the QC for the second officer, outlined a similar defence, saying the accused believed they had been carrying out a lawful order.

The panel, sitting in Goole, east Yorkshire, heard police had only been authorised to monitor protesters on the concourse outside Hull crown court to identify any who may have been involved in wrongdoing.

The inquest in 2000 concluded that Christopher Alder, a father of two and Falklands war veteran, had been unlawfully killed when he choked to death on the floor of the police station.

CCTV footage showed he received no help from officers as he struggled for breath, with his trousers and boxer shorts pulled down around his knees.

The officers thought Christopher Alder was play-acting. He stopped breathing after 11 minutes. Monkey noises were recorded on an audio tape as the handcuffed former soldier lay dead.

Janet Alder feared on a number of occasions that police had been spying on her after she started her campaign.

Details of the surveillance at the inquest came to light after a detective constable involved in the operation came forward to her superiors in 2013.

The then home secretary Theresa May had asked all police forces to search their archives after the Guardian revealed undercover police officers had monitored the campaign to bring the killers of Stephen Lawrence to justice.