The scenes in the film set at the Derby County training ground were actually filmed in Leeds at a football pitch ironically overlooking the Leeds United stadium.
Brian Clough is shown smoking in the film. His family maintain that he never took up the habit. However in a documentary made in the early 1970's Clough spoke about smoking too much and trying to quit. Perhaps he was careful about not smoking in the company of his family.
In the car scene where Brian Clough is going to try and sign Dave McKay, Pete (Timothy Spall) is seen eating a salt and vinegar packet of crusader crisps. Crusader crisps are a Netto own brand product, and Netto first opened in 1981, a few years after the film was set.
Derby are shown getting beaten 5-0 by Leeds in their first game against Leeds in the 1st Division. In fact they lost 2-0 in that first game, they lost 5-0 3 years later.
Who was managing Derby in the match that Brian Clough snuck into, if Dave Mackay hadn't been appointed yet?
A
Though it's not stated in the film, in real-life Jimmy Gordon took over as acting manager for two matches in-between Clough's resignation and Mackay's appointment, and remained with the club as Mackay's assistant until the end of the season, when he rejoined Clough at Leeds.