It varies but assuming you have a 5 days per week job an employer should be giving you 20 days paid holiday per year which could include public holidays. The key here is what your terms of employment say, as most employers exceed this amount. Also, if it was this employer who has been paying you for Easter for 20 years he needed to tell you in advance of this year that he was stopping doing this as it constitutes a change to your conditions of employment. Without this warning you may have a case based on custom and practice.
Ask your employer to reconsider nicely. Then raise a grievance. The CAB will be able to tell you more.