Although ACAS state that breaks should be taken in the middle of a shift, this is not law. ACAS is a guideline for all employers.
There is no law that states you should take breaks in the middle of a shift. You could in fact take your lunch hour at the end of a day, providing your employer agrees.
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, and you work for a firm employing 15 or more staff, then the
Disability Discrimination Act may also apply here. This states that employers need to make '
reasonable adjustments' to prevent disadvantage to disabled
employees. 'Reasonable adjustments' are not well defined in relation to this issue (so it would be a good idea to seek individual legal advice from your union or solicitor), but they could include greater flexibility in your hours to cover gaps, or availablity of time off (paid or unpaid) when needed.