Constructive dismissal feel free to e-mail me if you wish and i can give a union rep side
DOCUMENT EVERYTHING
From gov site
Constructive dismissal is when you’re forced to leave your job against your will because of your employer’s conduct.
The reasons you leave your job must be serious, for example, they:
don’t pay you or suddenly demote you for no reason
force you to accept unreasonable changes to how you work – eg tell you to work night shifts when your contract is only for day work
let other employees harass or bully you
Your employer’s breach of contract may be one serious incident or a series of incidents that are serious when taken together.
You should try and sort any issues out by speaking to your employer to solve the dispute.