THE 55 days of the play's title are those from December 1648 to January 1649 when Oliver Cromwell attempted to establish an English republic - and faced the dilemma of putting a king on trial when there was no legal procedure for doing so.
That confrontation is of course still of historical interest and in Howard Brenton's new play there is a certain frisson regarding the events that took place in the 17th century when England, for a short time, became a republic. Heady stuff indeed.
In the dispute between Cromwell's army and the Crown Dougie Henshall makes for an attractive and virile Cromwell. He's in modern commando garb while Mark Gatiss's effete and ghostly Charles I sports 16th-century costume - a visual contradiction that's a reminder of how the pomp and circumstance of royalty is a legacy that stays with us, despite parliamentary democracy.
The two leads are excellent, as are the supporting cast in the roles of Cromwell's advisor Lord Fairfax (Simon Kunz) and the King's aide the Duke of Richmond (James Wallace).
While Ashley Martin Davis's set design reflects the "modernity" of Cromwell's followers, with its office filing cabinets and shabby doors, the relationship between the visual signs and the action unfolding on the stage is unclear, since there is no organic link between the two - the signs hinder rather than illuminate events as an audience attempts to "read" them.
The action also becomes over-theatricalised as the fast-moving scenes, which change for almost every bout of verbal fencing, are pulled together by a plethora of mysterious characters charging back and forth through swing doors.
Drama about historical events often encapsulates in individuals the conflicts and contradictions of the time and Brenton has, in the past, successfully produced such characters drawn from historical events in Britain from the time of the Romans to Churchill.
Yet in this production the clunky staging makes an interesting historical confrontation between Cromwell and Charles a rather leaden encounter and the expository mode turns the evening into a history lesson.
While this pleases on one level, it is not the stuff of great historical drama.
Runs until November 24. Box office: (020) 7722-9301.