I notice on my 'host resources' page that airbnb are promoting the Masterlock key safe. I know it's very popular and I see many on the outside of houses. I had one of these at my airbnb holiday home and then discovered that my insurance company don't approve it. They do approve a couple which are available on amazon and are police approved - so I installed one of those instead. Just in case it's useful for anyone to know. It is probably worth checking with your insurance company.
This is the one I installed (and no - I have no personal £ interest in this company!)
https://www.amazon.co.uk/Burton-Preferred-Specification-Keyguard-Outdoor/dp/B019QR73QQ