Spooks star Nicola Walker says she’s a rarity in the series – a character who was written out, but not killed off.

“No one ever thought Ruth [Evershard] would return because she needed to have a new life and identity,” said Nicola. “She’s had this whole other life, and it’s not the one you might have expected. I thought Ruth might have gone on to a lonely life, in a bad job somewhere where her talents weren’t needed. That’s not the case.

“It’s rare characters can go back to this programme, even if they want to, because there’s a tradition of killing everyone off,” she said.

Details of Ruth’s reappearance are sketchy. The character left the show during the fifth series after allowing herself to be framed for murder to save her boss Harry, the man she loved. In return, he helped her fake her death in order to escape criminal charges. The last time viewers saw her she was sailing off to a new life, away from espionage and intelligence organisations.

The actress left the show to have a baby.

She said: “It’s all totally different since my day – my first day was very funny, I walked through the doors onto the grid and thought it would be exactly the same, but of course everything has changed. I kept walking into rooms thinking they were cupboards or toilets, but they’ve become other rooms since I left.”

:: Spooks is on BBC One on Wednesdays.