Thanks for the replies guys, I never thought that a tight spot in the chain could cause so much problem; I've always had a Scottoiler fitted, so I am very lazy at checking the chain!
Wheel alignment is OK, as I always install it myself after tyre changes etc. and use a steel rule to get it bob on.
Had a look at the chain last night and couldn't see a tight spot until I started checking link by link and found that it was every other one! I've given the chain a good clean, lathered it in engine oil and spent a couple of boring hours working each link until they all moved freely. I've left the tightest one (it's the joining link) sitting in a bowl of oil for the day to see if I can get it properly slick again. I'll give it a go tonight
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