IF a manager in England treats an employee in such a way that breaks terms with the employee contract, then the manager is likely to get sacked.
Neither employer nor employee can break contract without consent of the other party.
Thats the whole point of having a contract.
If what you said is true, then managers could do whatever they liked with employees, and this simply is not true. The managers have no legal rights whatsoever to operate in such a way that the employee contract rules are broken.