First the rules - in the list of types of types of aircraft forbidden to be used for a target in practice intercepts was a clear line item - “passenger carrying aircraft”. I used to get calls from ex-military captains saying they had put embellished in their flight plans but having to refuse unless they were freight only.
However, it was a rule prolifically broken. Back in the 1970s Air Anglia in and out of Norwich we’re outraged if they weren't intercepted - it was one reason many flew with them. The QRA when scrambled to north of Saxa awaiting Bears which went elsewhere would intercept transatlantic traffic to pass the time - the ****, as they say, hitting the fan when one crew sent in their MISREP claiming an intercept on a Korean 747 just a few months after the Russian shooting down of Korean Flight 007. The British sense of humour not going down well at SHAPE.
We would also scramble and intercept the charity BA flights with orphans at Xmas at their request. “And if you look out the left hand windows kiddies you’ll see a live armed RAF F-4!”
There were also numerous intercepts during exercises when real targets were in short supply. The order “target xxx range xxx, intercept with caution” being the indication that it was civil flight and to intercept accordingly. The tacit rules being that 1000ft separation would be kept so that it could explained as merely being in the same area rather than an intercept. Though comments from pilots such as “Identified, SAS DC-9, and there’s a woman in a red dress four windows from the back waving at me”, did tend to indicated the rules weren’t being observed. (The Lightning didn’t have Mode-C)
Reference the Concorde. I controlled a few of these intercepts in the short window in which they took place. Concorde flew a figure of eight in the North Sea at a constant M2.0 with the height varying around FL560-580 to hold a constant speed. The intercepts were mainly done by the CY and LU F-4s from nominated CAP points for a frontal shot, with obviously no stern conversion! The BK Lightnings also had a CAP point. The approved profile was also frontal with no stern conversion - accelerate at the tropopause for a 150 intercept, pull for a lead Redtop solution on the port missile, roll through 180 to reveal and fire the starboard missile and pull through to descend.
There was an occasion when a Lightning had a radio failure on reaching the CAP and did not abort. The pilot committed at the planned the time and did 180 stern intercept and claimed a kill. This obviously involved penetrating the MRSA whilst not under radar control. What height he achieved in the stern (Mx having a substantial height window) and whether it would have managed to reach the target is moot.
For interest the standard Lightning high flying supersonic stern target profile was, IIRC, the U3A. Target at M1.8 at FL560* for a 180 x 26 intercept converting to a 90 x 8 with the fighter accelerating to M2.0 in the crossing leg for a 1nm roll out.
*The legal Lightning ceiling was FL560 for flying clothing/oxygen mask reasons. Though it was routinely broken, with aircraft, especially in the last few months, exceeding 60K by up to 20K.
The French also used to send their Mirage IVs up as targets during exercises. We would be tipped of by LATCC as they headed north up the North Sea on their tanker and scramble a Lightning F-6 to do a frontal intercept as they headed south at M2.0. On one occasion Wattisham messed up and scrambled an F-3 with Firestreak. He was given a 180 intercept and rolled out at 3nm, closing to 1nm for the kill before, from M2+ and 60K heading south just north of B1, diverting into Coltishall because he had insufficient fuel to make Wattisham. Memory grows dim but I believe the pilot was S**** M******.