Hi Tracey
This comes under privacy laws, such as they are. What it boils down to is that anybody can take pictures of anything, anywhere, provided they are on public property and not used for nefarious purposes … and even then …
Even if you are outside someone’s property and take a picture of the inside, provided they aren’t nude or involved in sexual activity, you can get away with it.
However, if you are on their property, you need their permission or it is a trespass.
In short, the agent needs your permission and you could make that subject to removing personal items and a written undertaking that they will not be used in any other medium or for any other purpose.
You could withhold that permission but then you have to ask yourself if that would put renewing your tenancy at risk in the future.
The excellent and normally comprehensive Tenants Union website is silent on this. maybe you should drop them a line.