Queen Anne (Swan Theatre, Stratford-upon-Avon)

Helen Edmundson’s new play stars Natascha McElhone and Emma Cunniffe

Which Queen Anne would this be, pray? The RSC has already dealt with Anne of Cleves and Anne Boleyn. Maybe they're tracking down Anne of Austria, mother of Louis IV, or even speculating, Mike Bartlett-style, on a bizarrely unlikely future succession in our own royal family?

Nope. Helen Edmundson's enthralling, enjoyable new play homes in on the deliciously obscure Queen Anne of England, the second daughter of James II, who married George of Denmark, conceived and lost all seventeen of her children, oversaw the union with Scotland in 1707 and fretted through the Spanish war of succession. She was the last of the Stuart monarchs, succeeded by George I (not Denmark) in 1714.

It's her friendship with one of the most vivid characters of the day, Sarah Churchill, the Duchess of Marlborough, which concerns Edmundson; Natalie Abrahami's colourful, busy production in the Swan, provides two absolutely terrific female roles, seized on with flair and relish by Emma Cunniffe as the dumpy, serious-minded, sadly inclined Anne, and Natascha McElhone as the florid Sarah in red satin and high-piled coiffure.

Anne appoints Sarah mistress of the privy purse, though it's commonly thought they were even closer than that. Edmundson does not, however, fully follow that route, as Edward Bond did with Queen Victoria and Florence Nightingale in Early Morning; she's writing about power and betrayal between women, as well as the viper's nest of Jacobite plotting at the court.

There's a third woman in the shifting sands of political preferment, too, Sarah's cousin, Abigail Hill (a third impressive performance by a hungrily determined Beth Park), whose rise to favour challenges Sarah, while the latter's husband, John Churchill, Duke of Marlborough (Robert Cavanah), leads the British army abroad and gets into economic hot water (and an expenses scandal) at home while building Blenheim Palace.

The show is gussied up with a mixed bag of raucous songs and chorales (music and sound by Ben and Max Ringham, songs by Edmundson herself) which lower the tone impressively to link up with the lampooning commentary on the sidelines by none other than Jonathan Swift (Tom Turner) — his Conduct of the Allies pamphlet in 1711 had a huge bearing at home on the wars abroad — and Daniel Defoe (Carl Prekopp). Matters of state are steered, too, by Jonathan Broadbent's busy little acidulous leader of the Commons, Robert Harley, and Richard Hope's benignly decent (and therefore doomed) lord chancellor, Sydney Godolphin.

The first act is an over-dense stew and badly needs clarifying before coming back to the boil. But once, as another first-nighter said to me, you realise what the play is really about, the second act fully rewards your patience. There's a particularly fine scene between the childless, forlorn Anne and the newly pregnant pretender to her affection, Abigail, that sets up a marriage meltdown with the Churchills and a chilling climax of rejection.

Queen Anne runs at the Swan Theatre until 21 January