Generally speaking, if you are visiting the UK for a holiday and you are unlucky enough to need dental treatment, you will have to attend a private dental practice and pay for any treatment you receive. If, however, you are resident in the UK for a minimum of six months (because you are working or studying) you are eligible for NHS dental treatment.
However, it is notoriously difficult to find an NHS dentist willing to take on new patients, so it is advisable to register with a NHS dentist as soon as you find a place to live and ideally before you start having problems with your teeth.
A list of NHS dentists can be found on www.nhsdirect.nhs.uk or by calling NHS Direct on 0845 4647.