Mannix tells Whiteman to hide the recording for Shahara Hasan to find at a later date. When Hasan finds it (many years later), it is marked 'For DS Shahara Hasan', but Mannix only gave Whiteman her name, not her rank.
The Metropolitan police are shown with Thompson sub-machine guns when they fire upon DS Whiteman in the pub. Whilst the Homeguard in the UK had Thompsons during the second world war, the Metropolitan police did not, as they were non-combatants and only issued with Canadian bolt action rifles and pistols.
At 19.35 in, when Harker's last recording is being heard playing on the gramophone, the needle is not even on the record but off the edge of the turntable. Flat discs had replaced phonograph cylinders in the 1890's.
DC Hasan knew that Manix would use a phone to set off the bomb, so all she needed to do was call the bomb unit and tell them to jam communications instead of trying to convince him not to dial the number by playing the record.
However, this assumes encrypted mobile phone signals could be jammed effectively by the bomb squad (not their area of expertise) at short notice.
The last record we hear being played back had been recorded at 78rpm, but was played back at 33rpm. As the voice sounded normal, we should have seen the record revolving at 78rpm.
At the end as DS Whiteman is walking along a street in 1941 Whitechapel there are posters for an upcoming piano recital by Polly Hillinghead (the daughter of DI Hillinghead). The poster says the recital is to happen at Wilton's Music Hall in nearby Shadwell. The Music Hall closed in the 1870s and in 1941 the building was used as a mission hall by the Methodists. It became a music hall again in the 1990s.