Wearing a uniform or part thereof is not legally enforceable, but may be part of your terms of employment. If it is, then you need to do it ... or get another job.
I know it's a bit unjust expecting employees to pay for their own uniforms but schools do just that and companies are feeling the pinch. I know, for instance, that door stewards now have to pay for their own accreditation and stab-resistant vests, while restaurant staff in a local establishment have to buy and wear white shirt/blouse and black skirt/trousers.
Any required purchase of uniform IS tax deductable and you can claim it easily through your annual assessment.