New Sunday night BBC drama Undercover has millions of us gripped – and possibly a bit confused. But we don’t mind, as we get behind Sophie Okonedo’s thrilling character – a top-flight lawyer, unaware her husband of 20 years is an undercover policeman spying on her.

Shot between July last year and January, locations across London, in Merton, Southwark, Camden, Lambeth, Islington, Haringey and Kingston, were used in the six-part drama. It started this month.

Take a look at the trailer here. Lead character Maya, played by Okonedo, is about to become the first black Director of Public Prosecutions. Maya’s husband, Nick, is played by Adrian Lester. It should all feel eerily possible – writer Peter Moffat met Helen Steel, one of seven women who sued Scotland Yard after learning she had been seduced into a two-year relationship by an undercover officer.

“One of their biggest problems is that the law ruled it wasn’t possible to prosecute any of these men for rape, which is hard for them to understand because they were having sex with someone who wasn’t who they said they were,” he told The Observer.

FilmFixer manages the film office for these London boroughs. FilmFixer director Karen Everett says, “It’s significant that Undercover, with a very complex locations brief, made really good use of services in Merton, as well as Haringey and Kingston, outside the capital’s centre.

“As filming increases, it’s important to decant as much as possible to the outer boroughs, to take the pressure off the centre. This will be key to keeping filming sustainable.”

In Merton, a private home on Wandle Bank was used. As was All Saints Community Centre, where a donation of thanks will fund a day out for its visitors. The centre is dressed in the series as a secure psychiatric unit.

Driving scenes from Merton take in Wimbledon Road, Plough Lane, Haydons Road, Merton High Street, Kingston High Road, Dorset Road, Morden Road, Morden Hall Park car park, St. Helier Avenue and Rose Hill Roundabout.

Some of the most significant scenes were filmed in Southwark’s former Tower Bridge Magistrate’s Court on Tooley Street. In period scenes, of 1996, characters have been arrested and taken to a police station, where a fight breaks out. There are also scenes where a character walks free, out of the police station.

Also in Southwark, a character walks along Alberta Street onto Braganza Street checking that no one is following her. And the Blue Fin Building is used.

The series filmed Camden locations in Haverstock Hill, around Belsize Park and Steels Village, St Silas Place, the Shipton Estate, Burmarsh Estate playground, Marsden Street, Gillies Street, and Woodyard Place Estate, raising extra income for residents of Shipton and Burmarsh Estates. You’ll also see the Gipsy Queen pub on Malden Road, and Chancery Lane and Belsize Park tube stations.

A Lambeth home on Fieldhouse Road in Balham plays a key part. And filming also took place inside The Kings Arms on Roupell Street. In other scenes, two characters walk by Observation Point and Queen’s Stone Jetty, then move to Barge House Street and Broadwall. Another character walks out of the Thirsty Bear pub and towards Upper Ground. Very kind donations were made by way of thanks to Lambeth Estate Residents Association and Hatch Row Residents Association.

Lambeth’s Streathem Cemetery played a North London cemetery. And from Lambeth’s Charlie Chaplin Walk, a character takes the walkways around the IMAX and Waterloo Bridge, about to blow the whistle on some high-ranking officers. But she’s nabbed, injected with a substance and killed, to keep her from talking.

In Islington there was filming at Lady Margaret Road, a café on Junction Road and the Oak and Pastor pub.

And on a big shoot like this, a film crew needs a unit base – which can be tough to find in a built up city like London. But Haringey’s Finsbury Park provided an essential space when filming locally, as did Kingston’s Ashdown Road carpark.