This depends on what the written statement of employment particulars says. You must be given this statement within two months of starting work. The written statement should say clearly whether or not the handbook and staff rules are contractually binding and form part of the contract of employment.
Even if this is not clearly written, the rules may still form part of your employment contract.
Sometimes, the wording says clearly that some of the rules in the handbook are supposed to be contractually binding while others are not.
A rule that is part of your conditions of employment is a contract term and cannot be changed by either side without agreement. Where a trade union is recognised in the workplace, the change will normally be through collective bargaining.