The story of William Wilberforce (1759-1833) and Britain’s struggle to abolish the slave trade deserves something more substantial, and less confectionary, than what it gets here. Director Michael Apted and an impressive cast have plenty to show for their efforts, but the central strategies of Steven Knight’s screenplay seem distracting in general and misguided at best. The Welsh actor Ioan Gruffudd brings plenty of intelligence and charisma to the role of Wilberforce, but performance and characterization alike are diluted by a scenario that insists, repeatedly, on nudging the biography toward various clichés of inspirational melodrama. Still, the quality of the subject matter shines through as often as not. Confirmed Anglophiles will probably find it irresistible for its handsomely theatrical cast, and so much the better that this account of a pivotal moment in the history of Britain has the benefit of star performers who are from Wales (Gruffudd), Ireland (Michael Gambon), Scotland (Bill Paterson), Oxford (Toby Jones), Manchester (Albert Finney), Middlesex (Rufus Sewell) and Senegal (Youssou N’Dour).