well, for anyone under the ilusion that all the acts go through the same audition process, have a look at
this
"Favourites Scala are already an established professional act - and they even performed at last year's X Factor wrap party." so presuming simon cowell or at least one of his ilk was there it's not as if they were unknown to him.
"And the group was invited to enter Britain's Got Talent by ITV1 producers after the X Factor do last year.". so even if they went through the numerous auditions they were already known to the production teams. there was no way they weren't going to get through.
I don't think it states anywhere that you're not allowed to be a professional act, so in that sense they haven't done anything wrong, but the rest just confirms that it's all highly suspect, and that it's very unlikely anyone ever gets a fair audition.