I saw a movie a long time ago and I don't know much about it but I wanna see it again and can never figure out what it is...

it was set in Europe (England I think) and it had some school kids and their teach kidnapped by some ex cons/lunatics who stuck them in a cave. the kids escape and while tryint to get to the outside world come across a farm but the lunatics are there. the bad guy wears a Santa mask and they call him father Xmas while the others wear other masks... the kids end up making a kind of fort thing and battling it out with teh bad guys and it was a pretty cool setup as I recall. pretty gruesome stuff in some scenes but super cool as well.

anybody know this film??