ALISON ROWAT Bodyguard**** BBC1, 9pm)

LEST you thought David Cameron’s contribution to history was confined to Brexit, he turned up in Bodyguard last night in the kind of plot twist that would either have had viewers cheering or jeering the writer’s cheek.

As fans of Line of Duty know, that is the deal with Jed Mercurio, whose tale of a troubled protection officer has been giving the BBC the kind of ratings that usually only Strictly enjoys. Mercurio’s dramas are successful precisely because he sprints the thin line between thrilling and tosh.

Last night’s instalment, being the penultimate episode, had a tough job to do. Viewers still reeling from last week’s shock exit of Home Secretary Julia Montague (Keeley Hawes) might have thought there would be a decent period of mourning before we moved on. Forget it. As her protection officer David Budd (Scotland’s Richard Madden) barked when offered counselling: “Figuring out who killed Julia, that’s all that matters, that’s the only thing that’s going to make me feel okay again.”

Considering David was walking around with a dirty great burn mark from firing a gun at his own head, viewers might have wondered why he was allowed to keep working. Needs must was the answer. Like the Sergeant Brody tale in Homeland, Bodyguard hinges on whether David is hero or villain, up to his oxters in guilt, or the only good cowboy left. He has to drive events.

As he did so, questions began to pile up like a politician’s broken promises. Why hasn’t David revealed he knows the shooter? Why has Chanel the sacked PA turned up again? And why-oh-why-oh-why does David put up with the appallingly short battery life on his phone? As a colleague said when he had once again been uncontactable: “You wanna get a refund on that.” I’d like to see the phone shop assistant who would dare refuse him.

By episode end, David was going all out against those he suspects were responsible for killing Julia, aka “ma’am”, and folk were coming after him, gloves off. Everybody was after the missing tablet containing valuable data, and we don’t mean the complete box sets of Friends.

It was left to another ma’am, counter-terrorism chief Anne Sampson (Gina McKee), to pose the question of the night: “Who benefits?” At this rate, give or take your reaction to that last gasp twist, it is the viewer, ma’am, definitely the viewer.