Showing @ Royal Lyceum Theatre, Edinburgh until Sat 12 April @ 19:30 & matinees

It had to happen eventually. The Scottish arts scene has been relatively quiet when it comes to tackling the upcoming referendum and the possible end of Britain as we know it. Thank God for Union, which uses the original act of 1707 to drag the debate, kicking and screaming, to centre stage.

Refreshingly, and rarely for such epic and sweeping subject matter, the play is filthy; reminiscent of a post-midnight Black Adder the Third. Lords grasp women to their crotches, landlords piss on the oysters and everyone swears constantly. Historical dramas can make the mistake of preserving the past in decorous aspic, treating grand figures with kid gloves and in the process sucking the life out of proceedings. This isn’t a problem that Union ever encounters, and that’s all to the credit of Tim Barrow’s intelligent script and full-blooded characters; both of which veer superbly between humour and tragedy.

The acting comes in all shapes and sizes and is almost uniformly excellent. Big is the performance of Liam Brennan as the Duke of Queensbury, a whoring lush who wears his treachery with a great deal of style. Smaller is the work of Tony Cownie, as the chilling Earl of Stair the zealous butcher of Glencoe, but no less effective.

To turn exacting and pick the best from a very good bunch, the knock-out scenes are those that feature political machinations, rather than the human drama of the Scottish people. The incompetent plotting of English ministers in Queen Anne’s palace gets far and away the biggest laughs and moments spent in the soon-to-be-defunct Scottish Parliament are unrivalled in scope and execution.

A sea of wigs bob and nod along, as we watch five of the principal Peers – three for the motion, two against – battle and debate the future of their nation. Witty barbs compete with elegant, measured rhetoric, as we revel in skillful political language, now rarely used by our own beige overlords. It’s the crowning cherry on a play rich in colour, language and spectacle.