In a time when slavery was widely accepted, an idealistic young MP by the name of William Wilberforce dared to fly in the face of accepted morality and oppose the slave trade. He dedicated his life to its abolition; sacrificing his reputation, his health and risking his sanity to push a bill through parliament that was repeatedly denied on financial grounds. But with the support of England's twenty-four year-old Prime Minister William Pitt the Younger, his headstrong wife Barbara and former slave Olaudaqh Equiano, he navigated the backroom politics of eighteenth century England to end the slave trade in the British Empire.

Accomplished thought the visuals may be, the film lacks emotional depth. The real problem is that the film is too earnest, mythologizing Wilberforce to a certain extent and presenting him as some kind of saint (despite his dependence on laudanum). His political opposition are portrayed as two-dimensional bogeymen so lack the tang of authenticity and you never really see their side (twisted as it may be). We never see what the slaves go through first-hand and just hearing about it robs it of any emotional punch. Everything about the movie is a little too saccharine and cut and dried. It may be visually diverting and some of Wilberforce's publicity stunts and duplicitous strategies may be ingenious, but there is nothing that makes you feel for him. This makes for an informative, but rather dull hundred and eighteen minutes. And if anyone can explain the point of the tacked-on bagpipe performance of "Amazing Grace" I'd be more than grateful.

It is beyond my ken why Ioan Gruffudd was cast as William Wilberforce, with his lilting Welsh pronunciation. After all, the abolitionist is described in the script as "a real Yorkshire terrier". Gruffudd is also far too young and looks too insubstantial to play the doughty man that devoted his entire life to a single ideal. He tries his best, but he doesn't have quite enough fervour or weight to convince as the man of god trying to make life better for thousands. It doesn't feel like there is an internal struggle for him and that his turmoil, which makes him ill, is expressed solely through make-up rather than belief in the character.

Benedict Cumberbatch plays Pitt the Younger with humanity and gives the country's youngest ever PM a whiff of playfulness. But he is also determined, true, direct and most alarmingly for a politician - honest. Toby Jones is both his physical and moral opposite as the venal Duke of Clarence. He's an incredibly unlikeable little blob of lard; a painted, debauched prig with an inflated sense of self-worth, so he's ideal villain material. It's nice to see Rufus Sewell playing a good guy for a change as abolitionist Thomas Clarkson, but he still manages to be shifty and unsettling as the straggly-haired, whey-faced, melancholy realist who is a bit too keen on revolution. Meanwhile Youssou N'Dour is quietly dignified as freed slave Olaudaqh Equiano.