Searched the web and unable to find a solution. I have an umbraco site using IIS to host on a Windows server. Any ideas on approach to block users accessing site outside the UK? Htaccess approach would be too slow.... thank you in advance!
That's quite hard to do accurately, as you could have someone based in the UK using a European network provider, which means that they might appear to come from say Holland instead of the UK. It's also possible for people to spoof their location fairly easily if they really want to get at your site.
As Lex Li mentions there are plenty of commercial databases and tools for looking up a user's location, but the accuracy of these varies considerably, not to mention the fact that some of them only support IPv4. Any of these options are going to be slow though, as you'll have to check on every request. You also have to make sure you keep the databases up to date.
Another option would be to proxy your site through something like CloudFront or CloudFlare which both support blocking traffic by country.