Statutory annual holidays is 20 days, which you are receiving, plus the Public holidays of which there are 9 :
1st January
17th March
Easter Monday
First Monday in May
First Monday in June
First Monday in August
Last Monday in October
Christmas Day
St Stephens Day
Some people tend to believe Good friday is one , but it is not, it is an annual day unless your employer offers it as an additional day ,which often occurs.
point of information - your legal entitlement is to 4 working weeks leave not 20 days. Obviously if you work 5 days a week then the entitlement is 20; but if you work 4 days a week the entitlement is to 16 days leave.