With a few exceptions which almost certainly don't apply here (e.g. official secrets, indecent photographs of children or sexual voyeurism) anyone is free to photograph who or what they like as longs as they (or their camera) is:
(a) on their property;
(b) on property where they have permission for photography ; or
(c) in a public place.
For example, it's perfectly lawful to stand in the street, or in your own garden, and film people in their gardens or (through their windows) in their own homes. You don't need their permission and you don't need to tell them that you're doing it.
Even if you actually walked into someone else's garden to film them (or placed a camera in their garden) it would still only be a civil matter, not a criminal one.
Commercial premises using CCTV are subject to restrictions. The Data Protection Registrar (as he was then called) originally took the view that the same restrictions applied to private householders using CCTV but, following a court case which ruled on the matter, the Information Commissioner (as he is now called) has stated that those restrictions do NOT apply to private householders.
Chris