At the end of the trial, the camera shows Dave reacting to the verdict. But the people attending the trial are missing. Earlier shots of Dave showed the audience and the audience appears behind Dave later. The reaction shot obviously was recorded after the extras left.
In the court the magistrate has a gavel. These aren't used in British courts.
Magistrates are addressed as Your Worship, Sir, or Madam - not Your Honour. Hugh would have known this.
When Dave's wife is counting money at the concert, it's clear the bank notes are current Bank of England polymer notes, including £20 notes.
The film is set prior to when he opened the bank in 2011, the polymer £20 didn't come out until 2020. (2017 for the £10 note and 2016 for the £5 note.)
"Hugh makes his first trip to Burnley by car, but returns by train."
Yes, but Hugh had car trouble, so it can be assumed he decided to leave it in Burnley and return to London by train.
The story is set around 2011, but the Mercedes driven by Hugh has 2016 plates on it.
The bar lady in the Duck and Drake (situated in Leeds, not Burnley) pours 2 pints by holding the the pump handle but not actually pulling it.