If I buy an iPhone 6 from the US will it work in the UK?

On the US Apple store I can buy an iPhone 6 for £417 (649$) and on the UK Apple store I can buy an iPhone 6 for £539. If I buy it on the US Apple store and get them to send it to me in the UK will it work normally?

P.S I'm planning to get the completely unlocked version.

Apple Stores in US only ship within US but as you're from UK, you can't order directly from Apple US. If you have any relative or friend in US, he / she can help you with it. Also, you can get the phone at cheaper price if you go third-party. If you need more info on getting unlocked iPhone 6 at reasonable price cheaper than retail, mail me for more info.

That is $649 plus at least 10% local sales tax if delivered to a US address / purchased locally.
and
$649 plus 20% VAT for the UK, if shipped to the UK

US suppliers are required to apply destination sales taxes on behalf of the EU, if shipping to the EU.
(EU rules)

So you would not be winning anything
plus it would only have a US 90 days warrenty, extended to 1 years
Whereas the EU purchased one would have
EU warrenty - 2 years plus if puchased in the UK, additional Sale of goods act warrenties

NB the LTE bands in US and UK are different, so you would lose LTE compatibility
3G and 2G would work however.