How much do you know about the abdication of Edward VIII? Probably not much. King Edward took the throne when George V died and promptly resigned to marry his divorced girlfriend, his little brother picked up the reins of ‘power’, and life continued more or less as before. So far, so good. What you may know less about – I certainly did – is how reluctant the man who became George VI was to step into his big brother’s shoes. Afflicted by an overwhelming stammer, it was feared that he would be a complete loss to public life… until he met an extraordinary speech therapist who promised he could succeed where all others had failed. Their true story forms the backbone of an absolutely unforgettable film.

The year is 1925 and Prince Albert, Duke of York (Firth) must deliver a speech at the Empire Exhibition in Wembley; not only to the assembled crowd, but to the entire country via the modern miracle of the wireless. It’s an unprecedented disaster. Although his father (Michael Gambon) and brother David (Guy Pearce) have taken to the radio, ‘Bertie’ is afflicted by such a terrible stammer that he is totally incapable of speaking in public. The most eminent royal physicians have all failed miserably, so when Bertie’s wife Elizabeth (Bonham Carter) hears of an unconventionally brilliant speech therapist on Harley Street she persuades her husband to visit him in a last attempt to transform him into a public speaker.

Lionel Logue (Rush), an Australian with some very outlandish theories – he thinks smoking is bad for you, for God’s sake! – is deliriously eccentric and entirely disinterested in Bertie’s status as second in line to the Imperial throne. At first, Bertie refuses point blank to deal with the “jumped-up jackaroo” and his crackpot methods, but it soon becomes apparent that his wishes may become irrelevant. As the King’s health worsens and the Prince of Wales seems increasingly determined to marry his dreadful American squeeze (Eve Best), it seems ever more likely that Bertie’s worst nightmare will be thrust upon him, and Lionel is the only man in the Empire who has a shot at helping him address his crippling anxieties.

Sensitively adapted from real events, The King’s Speech takes some dramatic liberties with the precise chronology of Bertie and Lionel’s association but maintains the spirit of their relationship. Most importantly, it resists the temptation to give the film a ‘Hollywood ending’ in which George VI is miraculously cured – as Colin Firth noted at a recent press conference, he continued to suffer from a stammer (albeit greatly reduced) for the rest of his life.

Writer David Seidler (who drew many of the therapy scenes from his own childhood treatment for a pronounced stammer) has produced a touching script calculated to show the all-star cast to its best advantage. Helena Bonham Carter’s Queen Mum is overflowing with unashamedly self-indulgent regality, and supporting roles from Michael Gambon, Timothy Spall and Derek Jacobi are most welcome.

The real praise, however, must be reserved for the two extraordinary actors in the lead roles. Geoffrey Rush’s energetic, egalitarian Lionel is enchantingly disrespectful and endlessly sympathetic to Bertie’s plight, whilst Colin Firth is on course to finally win an Oscar for his performance as the man who would rather not be King. Vividly realising the epic struggle which Bertie faced on a daily basis just to force his words out, Firth’s performance brings to life a brave and supremely persistent man who puts his own wishes aside in his determination to become the monarch his subjects expect.

Simultaneously a period drama and a touching story of duty, commitment and dedication, The King’s Speech is unquestionably the best film to have appeared at this year’s BFI London Film Festival. I am conscious of the need to separate comment and opinion, but for my money it is quite simply the best film I have ever seen – well written, superbly directed and starring two actors at the very height of their powers and careers, it sets an almost impossible standard for either Firth or Rush to beat in years to come. Sublime.

The King’s Speech is released in the UK on January 7th. See it. Just see it.