Just create a user account at any of domain providers like godaddy(.)com and search for the availability of the domain and register it. you can choose any extension. not problem you are buying co.uk domain or co.in or co.cc domain.
The only restriction I can think of at the top of my head is the fact you arn't allowed private WHOIS. This can be an issue for some.
No private Whois and all details must be kept up to date, you can register .co.uk for £7.99 at Original Hosting
There is whois opt-out, though, so just your name is displayed. I don't see how this is a big deal (unless the person registering it is a scammer).
True, but when choosing a service provider price should not be the main reason. I would rather look at support if I was a customer.
I can confirm, managing 20-30 domains and 2 dedicated servers that FastHost's support are second to none.
Only your name will be in whois informations. If you want to transfer the domain you should pay 10 or 15 paunds and sent a ID copy to the provider.
It depends what the domain is used for. http://www.nominet.org.uk/uk-domain-names/about-domain-names/domain-lookup-whois/opt-out
Whilst that is true, it requires someone reporting you to Nominet. You can find plenty of commercial sites using it.
According to my knowledge Eurodns.com is the best domain name registrar for all domain name extensions. So - check them out!