Hello - not sure if this is the right site to post this, but here goes! I moved to Switzerland in May of this year without informing the UK tax authorities (I genuinley didn't know that you are meant to), I have be been working in Zurich ever since.

I am now considering returning to the UK (for personal reasons). I have recently heard that if you return to the UK within a year, you have to may 40% tax on what you have earned.

Is this true? If so will I have to wait until next May before returning without paying tax, or do I need to register with the UK tax authorities and then wait a year?

You have never permanantly left the UK, you need a full tax year absolute minimium so you need to be away until at least 6 April 2013.
If you have a home available, a wife & children still in the UK you won't have left, just been working away from home.

You are liable to UK taxes on your full world wide earnings, UK tax is self assesment, it's uptp you to pay, not for the revenue to ask you.....

Go to hmrc.gov and read the sections about leaving the UK, and how to fill in a tax return, especially the parts about residency. I know it's not the most fun reading you'll ever have, and it can be a pain reading all the separate notes documents, but really it's all there and in fairly plain language, there is even a number you can call for advice. It's not that hard and if you can't be bothered to put a bit of effort in instead of relying on the advice of random strangers on the Internet then you probably deserve to get tax audited!

Have a look at Sections 2, 3 and 8 of this advice from HMRC:

http://www.hmrc.gov.uk/cnr/hmrc6.pdf

In my case I became non-resident immediately after leaving the UK - I did not have to wait a year - but it depends in individual cases as to when they judge that your ties have been broken.

You were 'treated as non-resident', however if you returned without being away for a full tax year, you would then be liable to UK taxes on the income, you have to actually be away, your intention at the outset is not enough.

Thanks for the advice, I will read the docs.

I have no house, wife or children. So in a nutshell to "leave" the UK I just need to fill in an P85 form, and I can then return on 6th April 2013 without paying tax?

Yep thats right. You will get a statement from them about 8 weeks after the submission. Very very slow process. I sent in my form, didn't hear anything for 4 weeks so called up they said they had a back log and that post sent in July wouldn't be dealt with until September

I managed to get a refund though as I only earnt in April and May. Obviously if I were to return to the UK and get a job I'd have to pay it back if I go over the threashold.

I believe you have a contract & to be working abroad for the period, there is a very long revenue document with all the info, don't just read the simple one, it may not apply for various reasons.