Hi Colin - I think it must be a typo as both the mobile and desktop versions use the same validation and it validated OK when I typed it in here. Maybe there could be a space character before the first letter? Can you double check please by deleting your email address and typing it in again?
By the way, I've removed your email address from your post below as I we advise against sharing personal details like that on the forum.
The site on my PC happily accepts my log-in details, but when I try on my telephone (mobile site) it tells me to provide a valid email address. Whats not valid about my email address?