Full maeks and many thanks to FR and kwackboy for correctly diagnosing the cause of my troubles and saving me a load of grief in embarking on a wild goose chase.
I sourced a fuelpump and sender on fleabay and finally got around fiting it today. I'm delighted to say the bike is now running like new again (as it might with 970 miles up). Starts in half a crank, accelerates smoothly, idles evenly and generally is a pleasure to ride and listen to.
Its the most usable of my three bikes (GSX1400 and SV-650) and after an oil change I plan to use it regularly.
It was a lucky day when I doscovered this forum.
Thanks again FR and KB.