You've been posting, Dot, while I've been typing. I'll try to catch up!
Blu-Ray disc players produce an HD output signal, so manufacturers designed 'HD ready' TVs that could be used with them. At about the same time as Blu-Ray players were coming onto the market, Sky was also beginning trials of HD TV from its satellites. So 'HD ready' TVs were designed to have something else plugged into them (either a Blu-Ray player or a Sky HD box) in order to display HD programming.
Clearly anyone purchasing a new TV would also expect it to be capable of receiving Freeview. So manufacturers built 'ordinary' Freeview tuners into their sets. It was initially thought that it would be impossible to transmit HD signals on Freeview (because of bandwidth restrictions), so nobody had even thought of (yet alone manufactured) HD tuners for the Freeview system. It's now been found that there is some limited bandwidth capacity within the Freeview system, which can carry a small number of HD channels. The HD signals can't be handled by 'ordinary' Freeview tuners, so you need to acquire a new tuner. You can either buy a completely new TV set or (far cheaper) an HD set-top box.
Chris