Hi mopsy, Irish health insurance is only valid in Ireland and requires that you hold an Irish address for the majority of the year (allowances are made for long holidays and such). If you cancel you will have to serve your waiting periods again unless your company will recognise the time spent with any company you may join in the uk. Also if you decide to not tell your company and they find out they may cancel the policy back as if you were never covered for those 2 years. Basically if any information the have ie. address, is false they are entitled to void the insurance, this could also lead to them declining to quote you.
Be careful when deciding what to do here as most companies are very strict with things like this.
Best of luck. Bear