Thanks for the replies so far, everybody.
In reply to 'Graze' I have found a loose connection to the earth from the fuel pump which I discovered once the car had ground to an ignominious halt on a run earlier this week. Prior to this week the problem only manifested itself on pulling away, until the engine began misbehaving and then dying when going well, so I'm not sure as yet if this is a solution. The engine, however, has always pulled well when subjected to enthusiastic acceleration. I suspect, however, that the engine may be running rich so will be checking out spark plug colour following a good run, later this week. As regards the metering unit, this car is fairly new to me and there are no receipts for a recon or new metering unit, so suspect that this is original and hence has 85k under its belt. The injector spray patterns are good, though.
In reply to 'Alan', the problem is one of the engine dying through lack of pick-up and lack of power rather than stalling under applied load. However, I will follow your suggestion of checking out the butterfly linkages and of closing off the inlets.
In reply to 'Peter', I will follow your suggestion to check the ignition timing (and auto-advance) first. I have just bought new points and a red rotor arm from the 'Distributor Doctor' but, following the time-held edict of checking and changing only one item at a time, and in sequence, and following through each check and change to see what difference this made, I get the feeling that it may be a while before I get round to fitting these!
Many thanks, all, for your suggestions so far. Please keep them coming. I'll keep you posted on my progress.