If the contract states "40 hours but you will be required to work extra hours as required"..... 40 hrs is the minimum and any extra would be covered by overtime or days off in lieu. Beyond that 40 hr mark is NOT compulsary and no employer can just assume that the extra hours will be covered.
I think you would agree that to be expected to work 70hrs per week, every week, requires a re-think on the part of the contract and general working conditions of the company. This company IS in breach of the employment law as I'm sure any union would agree.
Seek the real advice from a lawyer, or the CAB for starters.