Yes, Mrs. Thatchers aircraft was BF, SZ was on standby, along with a 206. I don't know why that aircraft was chosen, as it was based in Aberdeen, but the guys in Aberdeen did a good job of tarting it up for the job. On its way down looking immaculate it staged through Yarmouth, where someone doing a turnround let off the floats. So Yarmouth had to spend most of the night repacking them, before it could be ready for the next day.
The Bristow sign over the door on SZ, was because all news cameramen filming people getting out, would studiously avoid the tail boom lettering. With letters over the door they could not ignore them.
I still have copies of letters from the Police deputy chief constable, and the conservative central office.