Went back over the images that were regarded as only average quality and re-exported them from LR at larger dimensions and larger dpi. Seemed to solve the problem. Updated the text, so captions and the odd description. Maybe could have done with some more supporting text, but the area is well known to the BCC audience so probably not necessary.
Pressed the button to upload and a number of warning messages came up about content overlapping the border areas. A bit troubling since I had used the provided templates all the way through. Analysis showed that the problem seemed to be the caption placeholders, so large-ish text boxes that lapped over the 'printable' edges of the page. reduced the size of the boxes to tight around the text and problem solved.
Apart from the main cover page that is. Instructions from the software suggested that it is essential to cover all of the cover area, including the border, for the purposes of printing. But it seems that if you follow this approach you end up causing a warning. Decided to go ahead with upload anyway, so we will see what happens.
Paid for book as part of the upload (£41) and about 10 day wait for it to arrive. Once I had done that I wondered if I should have sharpened the images for the print size? Oh well . . .
