"DucatiST4 - Is it something to do with the fact that in a double ejection the rear seat always goes first - this is so the rocket blast of the front seat going first doesn't cook the guy in the rear seat?"
It's to do mainly with ballistics. The aircraft and everything in it is traveling forward. If the front seat ejects first, then a few milliseconds later, the back seat is beneath the rocket powered chaos that is the first ejection. Ejecting second is bad karma, in this scenario.
Much better is the following Tornado F3 scenario: Command eject set to 'Both'. Let's say that the pilot is incapacitated, so the rear seater has no other survival option than to eject. Handle pulled, linkages unlock the canopy and fire the jettison rocket motors to remove the canopy (If a failure occurs, then MDC will shatter the canopy).
After a brief delay, the rear seat ejection gun fires, raising the seat up the rails, and out of the cockpit. At a pre-determined height, a lanyard attached to the cockpit floor triggers the rocket pack, boosting the seat to a safe height for parachute deployment from ground level.
After the rear seat has ejected, the front seat will eject and follow the same sequence as the rear.
If we acknowledge that the aircraft is traveling forward, and everything ejecting is traveling forward, but (relatively) backward from the aircraft, then the sequence makes sense.
Rear seat ejected first is swept back by the slipstream and post-ejection sequence occurs automatically.
Front seat ejects second, and actions follow those of rear seat.
With the tiny time delays between seat initiation, rear first makes sense. Front first would cause problems.