Now the fuss about Boardwalk Empire has died down - come on: it's boring, isn't it? - perhaps we can all very calmly consider The Promise
instead. Is Peter Kosminsky's epic new drama set in Mandate-era Palestine and 21st-century Israel fantastic? Yes, it is. Ambitious, well-written, superbly acted and expertly made, it is also provocative and challenging: the possibility exists that it might even change people's minds.

I am rarely equivocal, especially when it comes to Israel, but as I watched it - I have seen the whole series twice now, all seven hours of it - I felt even my allegiances shift and tilt. Would it have got made in the US? No, it would not. The people at HBO would no sooner commission a series as controversial and complicatedly nuanced as this than they would remake Emmerdale as a miniseries starring Sarah Jessica Parker and a pair of purple Hunter wellies.

Kosminsky, who is famed for his work ethic, writes as well as directs these days, and it turns out this is something he is rather good at. The Promise is based on years of research, and it shows: everything that happens in the series, however shocking, has some basis in historical fact. On the other hand, he hasn't allowed himself to be weighed down by his reading. At heart, The Promise is a gripping story, one that makes full use of Dickensian-style coincidences and secrets; the device Kosminsky deploys to link two narratives that take place 60 years apart is, delightfully, an old diary. Among his characters are a brave and moral soldier, a naive young woman, a handful of zealots and a lover who might not be exactly what she seems. What he has delivered, in essence, is a thumping great Victorian novel about the most intractable conflict of our age.

Erin Matthews (Claire Foy) is a student on her gap year. Sulky and impetuous, she has decided to join her friend Eliza Meyer (Perdita Weeks) in Israel; Eliza has dual nationality and is about to embark on military service.

In Erin's bag is her grandfather's diary, a fragile and ghostly burden she picked up only the other day, when she and her mother were clearing out her ailing grand­father's house.

Reading it, Erin discovers that her grand­father Len (Christian Cooke), a former British soldier, served both at the liberation of Bergen-Belsen and in Palestine, in the tense months before Israel declared itself a state in 1948 (the occupying British army was subject to a sustained and bloody terrorist campaign by Zionist groups). This diary, it is becoming clear, is going to change completely the nature of her stay in Israel. Already, she is no longer content merely to lie on an inflatable mattress in the middle of Eliza's parents' swimming pool. She is going to get herself a Middle Eastern education.

I love the texture of both narratives. Kosminsky bore the difficulties of shooting on location - it is unheard of for foreign crews to film in Israel - with the result that everything looks exactly right. In the sections set during the Mandate, you can almost smell the orange blossom, heady on the breeze; and 21st-century Israel feels clenched, like a fist. Even the dazzling white houses of Caesarea, the country's richest city and where Eliza's family lives, have an air of watchfulness. But it's the performances that make the thing. Itay Tiran, the great Israeli actor, is marvellous as Paul, Eliza's irritatingly reasonable peacenik brother. So, too, are Ali Suliman as Abu-Hassan, the tea-wallah at Len's base, and Haaz Sleiman as the former Palestinian prisoner Omar Habash, Paul's new friend. You believe in these characters absolutely.

As for Cooke, he captures with dignity and precision the unnerving combination of youthfulness and premature age that is the lot of the professional soldier; he drives his Jeep nonchalantly, with one hand, but his eyes suggest a man who is haunted. Cooke should win every award going. And as for the character he plays, Len is tenacious and brave, but these things come at a terrible price. In this sense, he is a metaphor for the State of Israel itself.

Let me warn you now: he's going to have you sobbing before this thing is over. Just like Erin, you will fall in love with him. And then he will break your heart. l

“The Promise" is on Sundays at 9pm