What’s the key to bringing home Nazanin Zaghari-Ratcliffe, the British woman who has been held hostage in Iran for almost six years? And how closely linked is Nazanin’s release to a tank deal debt more than 40 years old?

In episode 1 of Nazanin, former Today programme editor, Ceri Thomas, explores the origins of the debt, the apparent corruption which surrounded the deal which created it, and its long, difficult legacy. It’s a story which begins in the freewheeling 1970s when the need to ‘grease the wheels’ of big arms deals seemed barely controversial, and when the Shah of Iran and a notorious middleman known around Whitehall as ‘Mr 1%’ were able to pocket millions in commissions paid by the UK. And it leads back to the fate of more than one hostage today.

Presenter: Ceri Thomas Producer: Matt Russell Original music: Tom Kinsella A Tortoise Media production for BBC Radio 4