Do you really believe this, Ozzy?
" Well yes, most employers are within their rights to change the T&Cs of employment at any time, typically you know that up front when you accept a position with them."
Not so. At least not in any European or North American country. Your T&C is represented by a contract between you and the employer. If you accept a contract that allows unilateral variation, then the employer has that right. If you don't then the employer doesn't.
What astonishes me is how many intelligent well-educated people operate on myths and legends when it comes to one of the most important contractual relationships they have (while at the same time knowing PRECISELY what the warranty on their car says).
In fact we contribute to the incompetence of management by permitting them to get away with being incompetent in how they manage contracts of employment. It is a folie a deux. I have a personal story to tell about a company that routinely shafted its employees for years. One day one employee legally challenged what was their routine practice and took them for a six figure (plus costs) sum in the courts. Within a month the company cleaned up its act, to the satisfaction of the employees as well as the shareholders.