Hey guys,
Just wanted to give a definitive answer on this as it is a massive grey area! So I was in Korea for 1 yr Aug 10-Aug 11. I paid some minimal tax originally but submitted a proof of residency and then had any tax rebated. I've just completed a tax return for my time in Korea and had to pay UK tax. I'd recommend getting the proof of residency because even if you have paid tax in Korea, this amount is then deducted as foreign tax credits, which are an absolute nightmare to calculate so best to save yourself the hassle. The old law stating that if you are out of the country for 365 consecutively you are not liable to pay tax does no longer stand, HOWEVER I was told by HMRC that if you are out of the country for a full tax year i.e. April - April that you are not liable to pay tax. This does not seem fair as it means those entering Korea in March will more than likely be able to dodge this, while those entering in August like myself, will find themselves caught out. I went travelling after finishing in Korea for 4 months, however was told had I stayed out til April that I would not have had to pay! Doesn't seem right, I think they are still figuring things out.
However...I gotta say when speaking to people they've all responsed with 'What, you paid tax here? Sure you didn't live here!' Which I gotta say I agree with! So I'm sure there are loooads of people who just keep schtum about where they've been / what they've been doing. I had previously told student loans company what I was doing so I couldn't exactly backtrack but yeah...definitely something to think about.
Anyway hope this helps!!