@indysmith82…I’ve just installed a WordPress site at 123 reg with the same problem, no visual editor only HTML.
I managed to resolve it by going to the Admin screen, under Settings click on General, if there is an extra/stray colon ‘:’ at the end of either URL fields – remove it, save it and all should be fine.
It’s some conflict between 123 reg and WordPress. This could be the same for you.