What would you do…if you had to come up with £25,000 to save your child’s life?

Sherlock star Amanda Abbington has suffered her own financial difficulties in the past (she was declared insolvent in 2013 over a £120,000 tax bill), so she can certainly relate to the woman she plays in Channel 5’s new edge-of-the-seat thriller Desperate Measures.

When her character Rowan Taylor, a bank cashier, needs to come up with £25,000 fast she contemplates the possibility of robbing her employer, and Amanda isn’t entirely sure she wouldn’t do the same thing if she absolutely had to.

‘I say I wouldn’t but then I think what if, God forbid, something happened to one of my children and I was in a situation where I needed lots of money to help them,’ says Amanda, whose teenagers Joe and Grace are from her 16-year relationship with her Sherlock co-star Martin Freeman.

‘You don’t actually know what you’d do in that situation, and if you work in a bank and have easy access to the money and it’s a chance to save your son or daughter, you could make yourself believe it was for the greater good.’

In Desperate Measures, which runs over four consecutive nights this week on Channel 5, Rowan is facing uncertain times at Hanlows Bank where redundancies are rumoured.

Events quickly take a turn for the worse for her when her son Finn is forced into helping another boy named Conor to pull off a drug deal, but promptly mislays the £25,000 payment. Conor’s boss Kristoff wants the money back… and fast.

With no savings, a rented flat and up to her eyes in debt with her car, Rowan doesn’t know where to turn. Which is when she hits on the idea of robbing her own bank, with help from her disillusioned colleague Varisha (Sunetra Sarker).

Sound like a mission impossible?

Not when she can attach a secret camera to Varisha’s uniform to record the combinations of all the safes in the bank when she does the rounds with her boss. And when Rowan has an armed robber ex-boyfriend to help with the meticulous planning…

At one point evil Kristoff threatens Rowan’s son, and Amanda says a scene where Finn is suffering at his hands was hard to film, especially as for financial reasons the shoot took place in the Hungarian capital Budapest, a plane ride away from her children in England.

‘We had to keep filming that particular scene over and over again, and I was missing my own children so much at that point because I hadn’t seen them for weeks. I got very upset about that and by the end of it I was exhausted and sad. I had to leave messages for them telling them how much I missed them, and they were like, “Whatever! We love you too.” They were very good about it because we’re a little unit, and that’s the longest I’ve been away from them since I split up with their dad.’

The consolation for Amanda, seen most recently in ITV sitcom The Family Pile, is a four-part thriller that rips along at a cracking pace and will leave viewers wondering whether Rowan pulls off the heist – and saves her son – until the final scenes.

She’s obviously keeping schtum on the denouement, although she does hope viewers will have some sympathy for Rowan.

‘We tried to make her as empathetic, sensitive and nice as possible, to the point where she doesn’t have any nasty side to her at all,’ says Amanda. ‘She’s just a woman in really unfortunate circumstances who will go to any lengths to help her son, because he’s probably going to die if she doesn’t act.

‘I think the moral dilemma is whether she does the right thing or not by attempting to rob the bank. Personally, I think she’s doing the right thing for the right reasons, but whether the viewers will agree is another matter.’

Desperate Measures, Tuesday-Friday, 9pm, Channel 5.