Peter Morgan has started work on a follow-up to “The Queen” that will dig into former U.K. prime minister Tony Blair’s relationships with U.S. presidents Bill Clinton and George W. Bush.

The movie will focus on Blair’s reaction to the handover of power from Clinton, a natural liberal ally, to Bush, who came from the other end of the political spectrum.

“Peter sees this as a pivotal moment when the special relationship between Britain and America changed,” said producer Andy Harries.

Project will be the third film in Morgan’s “Blair trilogy,” which began with Channel 4 telepic “The Deal” and continued with “The Queen.” Michael Sheen is expected to reprise his role as Blair.

“Peter always hoped to do a trilogy to mark the Blair years that we’ve all lived through, but it’s been difficult to find the right point at which to look at Blair in power,” Harries said.

Morgan initially considered tackling the more obvious drama surrounding the run-up to the Iraq war, when Blair fatally compromised his own premiership through his wholehearted support for Bush’s invasion plans. But in the end Morgan decided that the roots of those events lay in Blair’s difficult adjustment to the transition from Clinton to Bush a few years earlier.

He’s researching the project with a plan to start writing by the end of this year. Harries and Christine Langan, the team behind “The Deal” and “The Queen,” will produce. No financing is attached, although with Langan working at BBC Films, that would be an obvious home for the project.

Harries already has another Morgan screenplay, “The Damned United,” in development with Langan at BBC Films. It’s adapted from David Peace’s novel about the legendary English soccer coach Brian Clough, with Sheen set to play Clough.

The project was originally due to be directed by Stephen Frears, who also helmed “The Queen,” but he stepped aside over the summer to be replaced by Tom Hooper. Pic is casting to shoot next April.

Morgan recently finished a rewrite of “State of Play” and a draft of the adaptation of John le Carre’s “Tinker, Tailor, Soldier, Spy,” both for Working Title. Working Title and Imagine Entertainment are also co-producing “Frost/Nixon,” Ron Howard’s movie version of Morgan’s stage hit.