Thanks for that one but I suspect that if I could understand 10% of that thread then I wouldn't have the problem in the first place

!!!
Some added info that might help those in the know ........
I've now played the DVD on a friends CRT television and the problem was exactly the same so that suggests the Plasma TV theory may be a red-herring !
I've also played it on my son's PS3, connected to the Plasma TV via a HDMi cable, and it played perfectly with no flickering.
I've tried re-encoding the source files with different software and that didn't improve anything. I've also tried playback at different screen ratios and that did nothing either.
Anybody know what all that might suggest ?