A friend in the UK is sharing a property with several other people, which includes one couple (of both British and South American origins), which I believe are the landlords. 

Yesterday, they decided to set up a webcam (including sound) inside the house, at the entrance, which they communicated to tenants in a WhatsApp message, saying it was for security reasons, especially as they had valuable furnishings in the house.

Putting the legality aside (as this is not the SE for that), my friend obviously has felt his privacy is being invaded, as while it is a public space in the house, it is still in his house.

The problem is how to relay this objection to the couple, especially since he feels they may simply "show him the door" and refuse to renew a contract for him to stay there.

My own suggestion was to offer to have every tenant contribute to a proper security camera monitored by a security company, but they could still "show him the door", and maybe not everyone would be willing to pay for that.

Disturbingly, the couple also made a remark based on the webcam footage about who a tenant brought home last night, and the comments didn't make it seem their concerns were about security nor unbiased.