The MOD hired Concorde from BAC (IIRC) for a supersonic intercept practice. It flew a circuit around the North Sea at M 2.0 as a target for each fighter wing in turn. It may even have been late 60s as I recall the Notam and exercise instruction but from 1970 I was overseas.
Interesting relative to first supersonic flight in Oct 69 which, curiously enough, was the month I first saw one whilst on leave in SW France.
Jack