I bought my phone in Hong kong but live in Uk, is the warranty valid?

Extremely unlikely there will be warranty.

http://www.apple.com/legal/warranty/products/iphone-english.html

"IMPORTANT RESTRICTION FOR iPHONE AND iPAD SERVICE.

Apple may restrict warranty service for iPhone and iPad to the country where Apple or its Authorized Distributors originally sold the device."

It's one of those tricky things. It can be limited, but it won't necessarily be limited. If you read the warranty terms around the world, the limitations are typically on iPhones, iPads (assumed to apply to cellular iPads), and Apple TV devices. These are all ones where there may be a legal limitation on distribution of devices meeting local law/regulation.

I've heard that maybe a defect in the battery or screen assembly might be covered. However, a lot of the major warranty issues are with the logic board, which is specific to region of distribution. Not sure about the camera as that can typically be replaced and is a more or less universal part. I suppose you could always ask.

I am guessing that anything Apple can do as an in-store repair (screens? batteries?) could probably be covered. However, many "repairs" aren't repairs but immediate replacements with identical refurbished models. Those models aren't frequently available in other countries, hence the limitations.

Limnos wrote:

I am guessing that anything Apple can do as an in-store repair (screens? batteries?) could probably be covered. However, many "repairs" aren't repairs but immediate replacements with identical refurbished models. Those models aren't frequently available in other countries, hence the limitations.

I certainly understand what the warranty terms say about "may be restricted". That being said, there's the occasional claim that someone got a local replacement device in exchange for a device purchased in another country. But I take it as more of a "one off" thing and certainly not anything where anyone should rely on an exception being made.

The one I'm thinking of is someone saying he bought his iPhone in Turkey, he was offered a US replacement at an Apple Store in California, but he's back in Turkey and upset that it doesn't seem to be able to use the device there.

The only way you will be able to get warranty service is to physically return it to Apple in Hong Kong.