VAT on SERVICES

Hi,

We are a service provider and provide our services to clients as follows:
a. Service to Irish organisations in Ireland. Invoice Irish company(vat 21.5%)
b. Service to UK organisations operating in Ireland not registered in Ireland for tax or vat other than PAYE. Invoice company in UK.
c. Service to UK organisations operation in UK. Invoice UK company for service completed from Ireland
d. Service to international clients with operations in Ireland. Invoice international offices for service completed in Ireland.
e. Service international clients with operations internationally. Complete service in Ireland but deliver elsewhere.


What rate of VAT should we charge on b., c., d., and e.?

Thanks.