THIS is the last and most epic of this year's swathe of plays to mark the 200th anniversary of the abolition of Britain's transatlantic slave trade, eclipsing even the heavy-going earnestness of Murray Watts's African Snow, at York Theatre Royal.

Rough Crossings would sum up the journey from page to stage of the very worthy adaptation by Dr Caryl Phillips, esteemed Leeds writer and academic long relocated to New York. It took eight months to turn Professor Simon Schama's history book into digestible theatre with a central theme and central characters whose travels and travails span more than 15 years as American black slaves fight for the British in exchange for freedom, but suffer abandonment in Nova Scotia and the false dawn of equal rights in Sierra Leone.

Maybe we are becoming too shallow in our theatre tastes, whether sexing up Greek tragedies, constantly redecorating Shakespeare or applying multi-media gloss through borrowing too much from other media. It comes as a shock to be confronted by a play that would not settle for that awful modern concept, accessibility.

Such a shock that Rough Crossings made me feel guilty, not so much about the trade, as we have spent much of this year being beaten about the head over Britain's past sins, but more that I found the production hard work on account of its arid intellectuality.

Yet I would defend the right of Phillips and Headlong Theatre director Rupert Goold to place great stock in that old theatre tool, the word, in two halves that each stretch to 70 minutes. The disappointment, however, is that Phillips subsequently takes such a didactic tone, despite his stated wish in his interview with The Press not to deliver a lecture.

At its crux is the battle between the white liberalism of the idealistic naval officer John Clarkson (Ed Hughes, with a strange accent full of soft letter T's) and the separatist zeal of Thomas Peters (Patrick Robinson).

Performances are intense, Goold's direction on Laura Hopkins' mobilised, tilting, seasick stage has impeccable shape and movement and vigour, but the play stays too long at the level of political debate - more Schama than drama.

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