This is a shocking situation. Your employers definitely are not allowed just to withhold your wages like that without even consulting you. First of all, how many other employees are in the same situation? Your first step should be to talk to your colleagues. If there is a union representative, you need to talk to them; but I'm guessing there isn't, or this couldn't have happened.

Have your bosses given any kind of official statement to the workers? You need to get every written document that you have on this subject. If there is nothing in writing, go straight to your employer and get them at least to give written confirmation of what you are owed and why it's being withheld. Then if you still aren't being paid, you can ask for advice from your nearest employment tribunal - details here - and for more general advice and support, also try the Citizens' Advice Bureau.