In the UK, depending upon when and where you install CCTV, you may be subject to various legal requirements. If you are installing it on a domestic property for solely non-commercial use, CCTV is subject to very little legislation. Planning permission is almost certainly not needed although it may be if you live in a listed building or a conservation area. However, you should always ensure the privacy of your neighbours by not letting your cameras intrude on their property.
CCTV for commercial premises are subject to much more regulation. The owner of the CCTV system must comply with the Data Protection Licence as well as being registered with the Information Commissioner’s Office. Depending upon where and how the CCTV system is being used, a Public Space Surveillance License may also be needed.
If in doubt, your professional CCTV installer or local council may be able to provide advice but for definitive legal advice on the matter you should always consult a solicitor.