Take it from me, the TRA (which is still active today) was unusually issued as 3000ft AGL. This even confused the Lancs police pilot who kept referring (in his exchanges with Warton ATC) to 3000ft altitude.
Blackburn was the centre of the TRA and the ground level varies from 500-800ft within the TRA. Manchester airspace starts at 4500 on 1013mb. So trying to stay legal above the TRA was not an easy thing to do.
And you have to question the whole reason why the TRA was established. It didn't even cover the Salmesbury BAe site where Dr Rice made her first speech - so anyone could have legally flown over this old airfield using the 500ft rule!
Later the same day there were no TRAs for Liverpool where the good doctor made further appearances. So why the Blackburn TRA ???
Nice shot of Lancs ASU EC135 on BBC News 24 yesterday! Couldn't see whether the pilot was one of the famed members of this Forum.......and he probably won't own up now given the "altitude" problem.
In answer to the original query, the Police do not police the skies - that is the job of the CAA. If anyone from CAA or DAP knocks on your door, pay attention. But to send a (presumably) non-aviation police officer to you - outside the TRA - is just not on. Draw the TRA and your site on your chart and file a complaint with DAP at Holborn.