More sex, please – it's British history! How the BBC plans to take on Downton

Upstairs Downstairs revival offers heady mix of class, politics, snobbery ... and lesbian affairs

The runaway success of Downton Abbey, ITV's award-winning period drama, has left residents of 165 Eaton Place brooding – both upstairs and downstairs. Now the BBC has unveiled a revamped and – as Downton's Dowager Countess of Grantham might say – rather racy revival of one of television's biggest hits, featuring an appearance by John F Kennedy and a lesbian romance.

Upstairs Downstairs, the story of the "upstairs" masters and their below-stairs servants, was hugely popular when its 68 episodes aired on ITV over five series between 1971 and 1975.

The show returned briefly on BBC1 at Christmas 2010, introducing Keeley Hawes as Lady Agnes and Ed Stoppard as her diplomat husband, but was soon outdone by Downton. The BBC's plans to come back with a six-part series then hit serious trouble when Eileen Atkins, the co-creator of the 1971 original with actress Jean Marsh, quit because she was reportedly unhappy with the direction of her character, Lady Holland. Marsh, 77, who reprised her role as maid Rose Buck, then suffered a stroke. Scripts were rewritten before Marsh's recovery gave her a reduced role.

Now the updated version of Upstairs Downstairs is returning to the same Belgravia townhouse, but otherwise it draws more parallels with Downton. Even the BBC's launch of the series was overshadowed, intentionally or not, by ITV's flagship drama – which announced that the Oscar-winning Hollywood star Shirley MacLaine will join Downton as the mother of Cora, Lady Grantham (played by Elizabeth McGovern).

Downton fans will find obvious similarities with Upstairs Downstairs when it launches next month. It is now 1938 and, as in Downton, the house is preparing for a war that will rupture the established social hierarchies.

Upstairs is written by Heidi Thomas, the "queen of Sunday night TV" and writer of such hits as Call The Midwife and Cranford. Her secret weapons include the arrival of Alex Kingston, formerly of ER and Doctor Who, as the sensual adventuress Blanche Mottershead, who hides a relationship with Emilia Fox's Lady Portia.

Thomas said her series, which dramatises Neville Chamberlain's talks with Adolf Hitler in Munich, and the future President Kennedy's 1938 visit to London, was both "epic and intimate".

Marsh checked herself out of hospital so she could return to filming. "I was absolutely determined," she said.