A few decades ago I was supporting QRA in the mighty VC10K, replacing another which had landed to refuel at Prestwick. Whilst in transit, SOC gave us the heads-up that a couple of Bears, which had earlier descended to low level on their way to the Bay of Biscay, were expected to return Northbound shortly....
A Shacklebomber then called up to say that they'd got a contact a long way West, which was heading North - suspected Bears. So we were cleared to fly direct across Irish airspace to nab the Bears, then shadow them waiting for a Phantom or two to join us. I queried the instruction with our nav, who was a Flt Cdr - he told me that there was indeed a high level agreement in place for such an event, but it was rather hush-hush...
So off we went, caught our Bears, refuelled a Q jet when it finally arrived, then followed the Russians until they left the 'area of interest'. Refuelled to max landing weight from the other VC10K which took over the task, then RTB'd direct to Brize.
Another great day out for the UK AD team - and top spot by the Shack crew!