The same file may not be the problem if the space assigned for the logo position isn't the same

e.g. some browsers will allow the image to break through the area available for it

At this stage it may be best to start again

Cheers
Paul

Right!
Three days later, wiped everything including the database, new url 109.123.108.118/~s9lsolar/, new database, new upload -
Same problem Small logo on home page, big on the rest of the site.
However, I seem to have overcome it by fiddling with the assignment, so it is now consistent, and behaving pretty well as I expect.
Problem remains that I don't actually know what I've done, and that I clearly don't understand how the home and default templates work in tandem, nor do I understand how assignment works.
More homework I suppose, and it's such a lovely day!
Thanks for your help so far Paul, but I'm afraid I'll be back for more.
Ian

No probs good luck with it

Cheers
Paul