Police turned up on the doorsteps of men and ordered them to hand over their DNA – for being gay.
Officers went to the homes of three men and demanded they be allowed to collect samples from them in case they were guilty of unsolved crimes.
The men were picked out because they had been convicted of the outdated offence of gross indecency.
And those who refused faced being arrested and taken to a police station for questioning.
The tactic was used by officers as part of Operation Nutmeg, the force’s move to solve old crimes by collecting DNA samples from rapists, murderers and child sex abusers in case they were responsible but never caught.
But those convicted solely of gross indecency were also grouped in the directive and received a knock on the door – despite national guidelines saying they should not be.
Two of the men were so concerned by the incident they called the Brighton LGBT Switchboard to see how it affected their legal rights.
The historic anti-homosexuality offence of gross indecency, which was famously used to convict Oscar Wilde, was repealed in 2003.
Natalie Woods, the service manager at Brighton LGBT Switchboard, said: “The fact that these men have been criminalised in the first place for consensual sex has had a distressing and adverse affect on their lives.
“To then be approached years later by the police requesting a DNA sample due to their unfair and no longer valid previous conviction can and does have a re-traumatising effect.”
Sussex Police confirmed three people had been contacted by officers but said all of the men then gave DNA “voluntarily”.
A spokesman said those contacted could have their DNA record destroyed if they requested.
But the force offered no apology for lumping the men in with rapists and child sex abusers in the search for offenders, or for any distress it may have caused.
James Ledward, the editor of Brighton-based G-Scene magazine, said it reminded him of the “dark days” when homosexuality was illegal.
He added: “The police have failed to follow the guidance. How could they get themselves in this position without questioning it?
“They should apologise to these people.”
A Sussex Police spokesman said the force was following national guidelines – despite the Association of Chief Police Officers’ guidance saying forces “should not seek to obtain a DNA sample from subjects who only have this conviction on their record”.
The spokesman added: “The Operation Nutmeg sampling process has not targeted any specific communities - we have approached all men and women who have relevant previous convictions.
“We would encourage anyone with concerns they may have a criminal record due to this repealed offence to request its removal. We can provide guidance to help with this process.
“Similarly, if any of the three men only convicted of this offence who have provided DNA samples under Operation Nutmeg would like to review their voluntary decision, we will be happy to hear from them."
In 1895 Oscar Wilde was prosecuted for gross indecency and was sentenced to two years in prison.
Thousands of other gay men were blackmailed, prosecuted, sentenced to prison, pilloried and shamed.
Alan Turing, who helped break the Enigma code, committed suicide shortly after his prosecution.
The law had been introduced to help convict people when there was not enough evidence of sodomy.
In 1967, Leo Abse introduced the Sexual Offences Bill 1967 which decriminalised consensual homosexual behaviour between men over the age of 21.
The offence of gross indecency was eventually scrapped in 2003.
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