2017 marks the the 50th anniversary of the 1967 Sexual Offences Act which decriminalised homosexual acts in England and Wales between adult males, in private. It’s very fitting then that this year’s BFI Flare: London LGBT Film Festival will open with the the world premiere of Against The Law, about one of the cases that helped lead to the partial decriminalisation of gay sex in England and Wales.

Directed by Fergus O’Brien and starring Daniel Mays, Mark Gatiss, Richard Gadd and Charlie Creed-Miles. Set in the 1950s, the film is based on Peter Wildeblood’s bestseller which tells the story of his affair with a handsome serviceman he met in Piccadilly and the devastating consequences of their relationship. Wildeblood (Daniel Mays) had been a celebrated and well-connected journalist on the Daily Express, with a range of acquaintances that included Lord Montagu of Beaulieu. The movie charts his journey from Fleet Street via public vilification to his imprisonment under the same legislation that sent Oscar Wilde to Reading Gaol. Mark Gatiss gives a chilling performance as a prison doctor charged with administering therapeutic measures to homosexuals acquiescing to the idea that they can be ‘changed’.

The importance of Peter Wildeblood’s case (jointly brought against him, Lord Montagu and Michael Pitt-Rivers) is that it brought the debate about homosexuality into the public domain. It led the way to the creation of the Wolfenden Committee on sexual law reform that eventually resulted in the passing of the 1967 Sexual Offences Act, which changed the lives of thousands of gay men with its partial decriminalisation of homosexual acts.

Director Fergus O’Brien comments: “Making this film for the BBC not only allowed us to tell a powerful and important story in the evolution of LGBT rights in this country but also to capture for posterity the voices of some of the men who lived through these dark days in gay history. Their story, and the story of Peter Wildeblood, are timely reminders of the difficult journey it took to arrive at the rights enjoyed by gay people today and why it’s so important that we safeguard them. I’m delighted and honoured that the film will be the Opening Night of BFI Flare”.

The film will also screen on BBC2 later this year.

As well as at the BFI Flare festival, the BFI will be marking the 50th Anniversary with a new season of screenings and events. This summer Gross Indecency will explore the pioneering – and sometimes problematic – depictions of LGBT life in British film and TV in the years immediately before and after the 1967 Sexual Offences Act.

The rest of the BFI Flare lineup will be announced next week. The festival runs 16th-26th March at BFI Southbank in London.