Thanks...it's a credit to the engineering that it runs as well as it does!

Thanks to all for the sage advice; a new plug socket, the penetrine, a cold engine and plenty of leverage meant the recalcitrent plugs obediently came out 1-2-3. Took it on a club run yesterday but I and another Series 1 were held up by an Alvis that wouldn't yield! Revving beautifully however...