Does my employer have to tell me about my right to join a union?

Yes. From October 2026, employers are legally required to provide all workers with a written statement informing them of their right to join a trade union. This must be given at the start of employment as part of your "Section 1" statement of particulars.

The Employer legally cannot promote any particular trade union.

You are fully entitled to have a trade union of your choice. The Workers of England Union advise to use Independent employment representative for the distinct advantages given to the employee.