He is breaking so many employment laws it's unbelievable.
He has allowed you to wear these shoes for five months without telling you they were inappropriate, that is known as "established practice" he has to give you fair notice of the change and an acceptable period within which to effect the change. (however wearing safety shoes in that environment would be considered BEST practice, from a health and safety and a Duty of care practice)
Swearing at you and intimidating you is against the acceptable working practices agreement that ALL employers must uphold
Gripping up an employee is common assault
Sacking anyone without a tribunal, and without suspending them on full pay pending said tribunal and giving the employee a chance to defend their position before sacking them is against the ACAS rules of practice. You do not need to belong to a union ALL employers MUST uphold and abide by the ACAS rules. . .it's LAW.
If you could get witnesses to back you with what he has been doing. You would have a rock solid case for unfair dismissal and he would have to pay YOU a very large payout.
the downside is that he would probaly end up closing the care home and that would affect the old people in care there.