Sixth form applications

I am a year 11 student and obviously the academic year a coming to an end pretty quickly. I have been applying to sixth forms as have many of my friends and most of us have applied to more than one. After most of the interviews, I went straight on-line and accepted the place to be told recently that you aren't actually allowed to accept more than one place?
I just wanted to know whether this was true or not?

Well, I accepted all of my offers for sixth form and then decided on choosing the one I most liked after I'd recieved my results. So, I think you can accept the condtitional offers (which lets them know you're still interested if you get the grades) after which you then can only choose one