t looks like KeySafe have updated their information about key safes and insurance.
https://keysafe.co.uk/faqs It's really difficult to find on this page unless you get their via Google or do a keyword search on the page. So I've copied it below:
"Each home insurance provider will have their own policy regarding the use of key safes. We recommend that users consult their insurance provider if they are concerned and switch if they believe they are being unreasonable.
Not all key safes are the same. We have found that with a C500 KeySafe installed, insurance companies are less likely to make amendments to home contents insurance.
If you have a C500 KeySafe installed, and if you choose to inform your home insurance provider, it is important that you make them aware that this is the particular key safe you are using. The C500 KeySafe has achieved Police approval through Secured by Design as a product that can help to reduce crime. It has been tested by an independent third party to a standard that the Police and the insurance industry recognise, LPS 1175 Level 1.
Advice from insurance companies includes this from the Managing Director of LV Home Insurance, Selwyn Fernandes: "If you must leave a key outside, use a police approved key safe and only give the code to people you trust"."