I used to work in UK and out of UK, and currently out. I left UK in 2002, though not a brit but no exception when it comes to tax.

You are liable to pay tax, but the real question is how much.

You only pay tax on the total income you earn in UK for the tax year. So when worked in UK for a few weeks before going abroad, you are liable for the tax of that few weeks you have worked in the UK
You also have a personal allowance for the tax year. Even if you work only a few weeks for the financial year, you are entitled to the full personal allowance for that year.

In short,
Say you work in UK for a few weeks before you leave , you earn 6000.
personal allowance = 4000 (dont know the exact figure now)
you are only liable to tax on 2000.
If tax rate is 20%, you pay only 400- if you have paid more than this , you can claim for a rebate.. I remember signing something which states that I wont be earning anything that is liable to UK income tax for the rest of the tax year when i made this claim. (When I started work, I used to time my start date and end date of my employment contract correctly so I can maximise this allowance)

If you have other investments etc, then it gets trickier. Say you rent out your property, and have income via savings/shares etc.- you are still liable for UK income tax on those income. In which case i suggest a financial consultant.