Had a look at Lathams but it was not clear if the door came with a door frame, locking system etc. Looking at GRP Doors site it’s very comprehensive showing all the accessories and costs. That said, I did like Latham steel doors for the security as you point out.
Latham doors come complete with absolutely everything, frame, locks, handles, everything, even a fitting kit if selected as an option including the drill bit for the wall. I wouldn't use a mobile device for their website, a laptop or PC is preferred.