Just like to say thanks to all who replied. Couple of things i think i'll
look into after all the suggestions:-
1) clipless pedals might well help - been thinking about trying some of
these. Suspect my foot is moving around a bit.
2) Longer seatpost - might well do but have been considering a new bike for
a while so maybe a 21" inch would be worth trying. Might be an idea to hire
one if possible and see if it makes a difference. Trouble with longer
seatpost is eventually i'll get it so high i'll start getting backache
reaching for the handlebars ( mind you backache would make a nice change if
it sorted out my knees for a while :-) ).
I do suspect i need to get the saddle higher somehow, i just must be a funny
shape. I already have it so my heel with shoes is just shy of the pedal at
6'0 clock but i can still touch the ground with both feet ( tiptoes mind ).
For info - did see a physio about 6 months back and explained what was
happening - she had a look etc. and said she couldn't see any problems but
there is no doubt my knees suffer ( twinges/crunching) etc. when i cycle
regularly.
Once again thanks to all -determined to sort this out as i'm not giving up
my only form of exercise - let you all know if i make any progress.
Jon.