UCAS Extra?

Hi,
I'm a EU student (not from the UK). I have applied to uni through UCAS and I'm still waiting for all unis to reply. I had a look at UCAS Extra to see what courses are available as a backup in case I don't get accepted anywhere and I've noticed there are courses from some very good unis (eg. Imperial, King's, UCL Edinburgh) and I saw courses from Cambridge too. Now, I'm not familiar with the system and I was especially sceptic to see Cambridge and Imperial in Extra so I was wondering how this works.