There isn't a general legal requirement for your employer to give time off for medical appointments. Whatever entitlement you have to time to visit the doctor will be governed by your individual employment contract.
You should check your contract and staff handbook, as this may specify what the regulations are in your workplace. Some employers may require you to take annual leave, or take the time unpaid. On the other hand, many employers will be flexible on this, and it may be worth asking your employer if you can make up the time later.
If you have a disability which requires you to make regular medical visits, then the laws against disability discrimination (now contained in the Equality Act 2010) may also apply here.
These require employers to make 'reasonable adjustments' to prevent disadvantage to disabled employees. It would be a good idea to ask for advice on what adjustments might be appropriate in your case, for example from your union, a Citizens Advice Bureau or a Disability Employment Adviser at your local job centre. 'Reasonable adjustments' are not well defined in relation to this issue but they could include greater flexibility in your hours to cover gaps, or availability of time off (paid or unpaid) when needed.
