Other mistake: After the attack on the police station we see a train passing by in front of the fire. The shiny train reflects the flames in a way that could only be caused by another fire for which there is no evidence. (00:16:20)
Suggested correction: We do not know that the IRA didn't set another fire. They may well have, but it wasn't shown. As there is another fire reflected on the train, then it must have been set, but the viewer was not shown the details.
Other mistake: When Kitty reads Michael's letter from England to Harry, there's some strange smoke arising from behind their chairs. (01:19:40)