Chris O'Dowd is insisting that his new sitcom Family Tree is unlike anything he has done before.

The actor plays the lead role of Tom Chadwick in the HBO show, which is directed by This Is Spinal Tap star Christopher Guest.

Chadwick travels across Britain and America as he searches for his estranged family in the eight-part series.

Describing the role - which involves scripted work and improvisation - O'Dowd told Empire: "It's very reactive; unlike anything I've done."

Guest said that he was happy to work with O'Dowd, whose previous credits include hit movie Bridesmaids and TV shows The IT Crowd, Moone Boy and Girls.

The director - whose CV includes the comedy Best In Show - said: "Is it going to be epic? That's a big word. Let's just say it's a delight to finally work with Chris."

Fred Willard (Anchorman) and Tom Bennett (PhoneShop) will also appear in the sitcom, which will air on BBC Two this side of the Atlantic.