Tommy Lascelles (Paul Brooke) is depicted as the Private Secretary to Bertie from the start of his reign, and certainly from the beginning of the war. In fact, though he had been an Assistant Private Secretary since shortly before King George V's death, he was only promoted to the full role (directly dealing with the King and his boxes, for example) as late in the War as 1943. He remained at post for the rest of the King's reign, several years after retirement age, and into Elizabeth II's first year as Queen. It's best to think of the role as combining two real-life people (Sir Alec Hardinge and Sir Alan "Tommy" Lascelles) into one.
Denis Lill (Clement Attlee) previously played King George VI in The Gathering Storm (1974) and his paternal grandfather King Edward VII in Lillie (1978).
In a career rarity, Robert Hardy appeared in the film but not as British Prime Minister Winston Churchill. Instead, he played Churchill's counterpart, U.S. President Franklin D. Roosevelt.
This film tells much the same story as The King's Speech. There is considerable overlap among the cast as well. James Wilby shares the role of Prince Albert with Colin Firth. Wilby, Firth, and Timothy Spall appeared together in the 1985 TV movie Dutch Girls. Spall, who played Churchill in The King's Speech, appears in the Harry Potter films with both Robert Hardy and David Ryall. James Wilby appeared with Helena Bonham Carter in Howards End. Alan Bates appeared with Helena Bonham Carter in Hamlet, in which he played Claudius. In the 1996 film of Hamlet that role was played by Derek Jacobi, who also appeared in The King's Speech. Michael Gambon played George V in that film. Gambon, Bates, Jacobi, and Eileen Atkins all appeared together in Gosford Park. Oliver Ford Davies, who shares with Jacobi the role of Archbishop Cosmo Lang, appeared with him in Revelation and Philby, Burgess and Maclean.