Saskia Reeves on Slow Horses, navigating ageism, and screen chemistry with Gary Oldman

That depends, in large part, on an anxious cardigan-wearing woman in her 60s. Catherine Standish – recovering alcoholic and erstwhile assistant to Slough House boss, the flatulent and ferociously brusque Jackson Lamb.

It's Standish who takes the full brunt of Lamb's mocking jibes and the horrors of his woeful personal hygiene regime. Yet, of all his relationships, this is one that really seems to matter to him.

"Gary [Oldman] and I talked about this right at the beginning," Reeves explains. "They each know where the other one has come from and understand each other. I think of them as analogue characters as opposed to digital. They're intellectually similar – I wouldn't say she's equally as intelligent as him, but she has an emotional intelligence."

When we last saw Standish, she'd been rescued from kidnappers and had discovered that her former boss at MI5, Charles Partner – whom she'd idolised – had worked for the Soviets during the Cold War and had been killed in the bath by her current boss, the odious aforementioned Lamb.

Oldman, she says, isn't physically unpleasant in real life. "No! But there are times when I read the script and go, 'They're not going to go there?'" says Reeves, whose previous television credits include the BBC's Wolf Hall and Shetland. "Gary is being incredibly brave in it. He's not using padded suits; he’s putting himself out there, and that encourages me, too."

Oldman may be pleasantly fragrant in real life, but Slough House, Slow Horses HQ, is not. "The effort that goes into the production design is so well thought out," Reeves reveals. "There are cobwebs on the windowsill, the radiators are rusty, the kitchen is s**t and the fridge smells – it's really brilliant."

Reeves, who turned 63 in August, is three years younger than Oldman, and has been aware of his remarkable talent from the beginning of her career. "Gary was one of my contemporaries when he was still living and working in London. I saw him at the Royal Court. I watched all his early television stuff. I knew him to be this exciting, different, challenging, brave actor, and I loved his sense of freedom. He didn't seem to be hampered by all the other stuff we were dealing with as we were trying to become actors."

Her Standish is restrained and quiet but retains a core of moral rectitude; qualities that are underappreciated by some of the show's male characters. "I suppose that's part of being a woman of that age when your hair goes grey and, actually, you do become a bit invisible," says Reeves.

"There were moments when Roddy Ho [Slough House resident computer geek and sexist creep] is so dismissive of Catherine you think, 'You have no idea how experienced this woman is, and if she wasn't so damn underconfident and struggling with her own demons, she'd be a much better spy than all of you lot.' I love that element of her character. The things she can accomplish, the strange excitement that she gets for being part of the action."

Does she like playing an older woman who, in her own way, overcomes the sexism and ageism of those around her? "I think as a woman of a certain age in any industry, acting included, as you get older, it's hard to make your voice heard. It's hard to be seen the same way."

Yet this is a show that celebrates its older characters. River Cartwright, played by the excellent 34-year-old Jack Lowden, may be the heroic lead, but Slow Horses belongs to Reeves, Oldman, 77-year-old Jonathan Pryce as Cartwright's grandfather, David, and 64-year-old Kristin Scott Thomas, who plays Diana Taverner, the deputy director-general of MI5.

These are, I suggest, the sort of names that mean a show will do well. "I heard Gary and Kristin were doing this, and then we went into lockdown in 2020," she says of the early days of Slow Horses. "It was the summer, and I was getting very anxious and nervous about the future; how we were going to manage, what was going to happen.

"Then the voice in my head went, 'Saskia, you've been cast in a series with Gary Oldman. They will make it happen. They've got Gary. They're not going to let him go. It'll be fine.'"

Four seasons later, everything is still fine, thanks, in large part, to the chemistry between Reeves and Oldman. "Often, you hear about actors in series that go on and on, it gets a bit tired and formulaic. But the new series is so good. Watching it, I thought, 'Wow, this is brilliant. They're not going to expect this.'"

Slow Horses season 4 will stream on Apple TV+ from Wednesday 4th September – sign up to Apple TV+ now.

Check out more of our Drama coverage or visit our TV Guide and Streaming Guide to find out what's on. For more from the biggest stars in TV, listen to The Radio Times Podcast.