Thanks.
I have to say I couldn't find the "Submit..." button selection you mentioned, but I could have been looking in the wrong place. I checked all of the settings on the Checkout tab of the Config settings.
So I started messing with the Login button/step in the workflow, since I'm using Guest checkout I tried removing it and also moving its position around a bit but I couldn't advance beyond the initial Cart step. However, after returning this Login step back to the Address step (but below the Address step) the issue seems to have resolved itself... I think. Not entirely sure why though.
So the Login tab/step in the checkout has changed to Address instead, which is fine, but it seems to take 2 clicks, of the now correct Next button, to advance the process if a Shipping address is added... why would this be?
I may have listed the wrong site URL? Try this one, it does have Products now...
peakeperennials.co.uk/shoptest/index.php/shop-all-plants
I've also attached the step workflow, if it helps.
Regards