Factual error: Chief Superintendent Hilton wears the ribbons of the General Service Medal (awarded for military service in a combat zone, most commonly in Northern Ireland) and the Police Long Service and Good Conduct Medal (awarded for twenty years' service), but not the Golden Jubilee Medal (awarded to all officers with five years' service in 2002), which he would also have. When he reappears in Series 4, he is wearing the Golden Jubilee Medal, Diamond Jubilee Medal (awarded in 2012) and Police Long Service and Good Conduct Medal, which would all be correct, but no longer has the General Service Medal.
Other mistake: The team blow the flat door in (no. 56/59) with charges applied to the door. When Arnot arrives, the door is intact on the floor, complete with the door number, including the loose 6/9. This is pivotal in revealing that they have the wrong flat! Stairwell sign indicates flats 50 - 59. Regardless of which way they approached, they would have passed other flats and observed the door numbers. (00:02:28)
Factual error: British prisons do not have glass partitions between prisoners, and visitors and visiting facilities are not in closed cubicles. Visits are carried out in open rooms with other prisoners and their visitors, prisoners sit at individual tables with their visitors and touching is usually allowed within reason.
Factual error: Superintendent Hastings does not wear the ribbon of the Diamond Jubilee Medal (awarded to all officers with five years' service in 2012), although he does wear the Golden Jubilee Medal (awarded to all officers with five years' service in 2002) and the Police Long Service and Good Conduct Medal (awarded for twenty years' service). Other characters do wear the Diamond Jubilee Medal, so this is obviously after it has been issued. In subsequent series he is wearing the ribbon.