[anotheracctfo]

Sure you can sue them. The employee contractor line is a big part of labour law, and can affect UK mandated legal protections and benefits. The only problem is that a labour lawyer starts at $400/hr. One way to get around this is to band together with other contractors in your organization and pool your money to purchase a lawyer. We typically call this a union. I was high up in my union and signed some very big cheques to lawyers.

Of course that's hard so you should just get a new job.