Many thanks James.
I've taken the under construction thingy off (I think) so you should be able to view the page in question thus (I hope)
http://www.racingtourstore.com/product/5-nights-derby-tour-budget
The thumbnails in question are appearing below the main product image. A closer inspection of them seems to indicate that they're displaying the middle section of the image I want to display. They're fine when you click into them, but instinctively I feel it's something I've done in the set up. Originally I tested one out and it displayed fine, so I assumed I'd come back to it and finish it off as a last job. Now however they're displaying as a thin strip.