If you are a resident of the European Economic Area (EEA) country (Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Republic of Ireland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, The Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, UK) or Switzerland, you are entitled to treatment in another EEA member state. This right is regulated by the case law from the European Court of Justice (ECJ). According to the ECJ, patients are able to get any type of healthcare services in another EEA country. Moreover, patients are entitled to their costs reimbursements.
In the UK the system of reimbursements for medical travel is regulated by the National Health Service (Reimbursement of the Cost of EEA Treatment) Regulations 2010. According to this document, the UK residents are entitled to reimbursement which is equal to a price of a similar procedure in the UK. Costs exceeding this price have to be covered personally. Additionally, the Secretary of State may limit reimbursements if the medical procedure is available at the same time in the UK.
All in all, you have the right to get a reimbursement of treatment abroad if there is no possibility to get the same treatment in your country within a medically acceptable period.