norodnik
...Did you need all 4 reheats to go from 0.95 - 1.7 ?...
No.
Two reheats were the minimum for transonic acceleration, however due regard would have to paid to the additional fuel usage with one or two reheats failed.
...If you got to 1.3 and then one or more failed could you continue (albeit with slower acceleration ?)...
Yes, as above, whilst remembering the 15 minute time limit on the use of reheat.
...I presume if you were unable to get the things lit at 0.95 you just turned round and went home again ?...
Yes, once you were convinced that at least three were not going to light up.
...The procedure would take around 90 mins so would you need to burn off fuel or already be at acceptable landing weight by that time ?...
Not something I ever had to do, fortunately, but even so, 90 minutes would seem somewhat excessive to me, given that the aircraft would still have been over the Bristol channel. On a transatlantic sector, fuel jettisoning would have been necessary to get down to 130,000 kgs (for a fuel saving landing) or 111,130 kgs (MLW) if the nature of the failure precluded a fuel saving landing.
...once when aboard at about 50K-55K feet the aircraft rolled I would estimate 3 degrees to the left and then came back level again almost immediately...what might have cause such an event (I would guess an airflow issue with intake or engine ?)...
Any number of things could have caused this, but probably the most likely one is the one you suspected, a (transient) intake problem.
Best Regards
Bellerophon