"Two members of the Lothian" joke

Two members of the Lothian and Borders traffic police were out on the
Berwickshire moors with a radar gun recently, happily engaged in
apprehending speeding motorists, when their equipment suddenly locked-up
completely with an unexpected reading of well over 300 mph. The mystery
was explained seconds later as a low flying Harrier hurtled over their heads.
The boys in blue, upset at the damage to their radar gun, put in a
complaint to the RAF, but were somewhat chastened when the RAF pointed out
that the damage might well have been more severe. The Harrier's
target-seeker had locked on to the 'enemy' radar and triggered an
automatic retaliatory air-to-surface missile attack. Luckily(?) the
Harrier was operating unarmed.