@Alexandra1169 If you're required to collect guests' home addresses in order to comply with your local laws, you should state very clearly in your House Rules that this is a condition of booking, and preferably reference the law that you are upholding.
However, your policy would appear to contradict the government guidance published here: https://www.gov.uk/guidance/guidance-on-holidays-in-areas-with-local-coronavirus-covid-19-restrictio... (my apologies if this is out of date)
If you live inside an area with local restrictions, you can go on holiday outside that area but you should only socialise indoors with members of your own household or support bubble
You can only stay in a private home - which includes self-catered accommodation such as holiday cottages, apartments or boats - with members of your own household or support bubble
My understanding of this is that you can host guests from a local lockdown area who are from a single household. I haven't been able to locate any materials requiring hosts of Entire Home properties to discriminate against guests based on their postal address. You might have to collect some personal data upon arrival for contact-tracing purposes, but unless your specific locality has a separate rule for accommodation providers, it appears that you're out of your jurisdiction here and may well be violating the guests' privacy.
If this is your personal risk-management strategy - well, Neil deGrasse Tyson put it best, "it's like having a non-peeing section in the swimming pool." If you're choosing to host in a pandemic, sorting guests based on which postcode they live in is an exercise in futility - especially considering that one's residence still doesn't tell you where else they've been in the last weeks or how strictly they've been complying with the laws themselves. What it comes down to is, your whole island is high-risk, and any guest who crosses your doorstep might be a contagious carrier of the virus, regardless of their postal address. If you don't feel that your current protocol would allow you to host an infectious person safely, it would make far more sense to suspend your hosting operation than to attempt your own foreign policy.