I taught in a private school for a while. In England and Wales the law says that your employment “contract” is simply the verbal, written, or implied agreement to work there and the document enumerating the details — the written statement of employment particulars which is basically the thing you or I would call “the contract” — doesn’t have to be supplied until up to two months after you’ve started work.

My employment particulars came the day of the two month deadline. They included a clause that said that the school had the final say on any claim brought by a pupil or their family against me for loss or damage and that any compensation would automatically be deducted from my salary. Unsurprisingly, I did not agree to this clause and did not sign the document! The school also refused to negotiate and I worked there for two years in a kind of contract limbo.

I’ve gone back to being a SWE now. I was lucky to not be beholden to one industry like my fellow teachers were. I can completely see how a sub-postmaster, without a fallback career, can get cornered into accepting some ludicrously unfair terms.

That is pretty awful, and although it's legal to argue over contract terms, including the employer being completely obstinate and your only option being not to agree, you were right not to back down and accept such a one-sided negotiation.

In the case of SPMs, as the Post Office holds all the cards, they can kick out anyone not willing to accept the unfair contract... like the Mr Bates at the centre of it all, who lost his position as SPM after standing his ground and refusing to accept liability for blatantly false losses attributed to his branch by the Horizon software. Not every SPM was lucky enough to be in the same position as him.