Your front garden?
Typically, a public area where anyone can see what you do.
Or your back garden?
An area where you might reasonably expect privacy.
As a general rule:
Home / private CCTV systems are not covered by the Data Protection Act (do not have to comply with it).
There was a case a few years back where a doctor took the neighbour opposite to court, IIRC because their doorbell camera was covering his house opposite, and won (the system owner was fined).
It was a typical neighbour dispute that got out of hand / escalated, and the claimant had deep pockets ...
The Amazon devices were found to invade privacy and break data laws in a landmark UK case.
www.bbc.co.uk
Dr Mary Fairhurst claimed her neighbour's cameras left her feeling as though she was under "continuous visual surveillance" as a judge ruled that the footage captured breached Data Protection laws
www.dailystar.co.uk