Neil
Not strictly true. If you have any assets, such as shares or property in the UK on which you earn income, then your salary is liable for UK tax. Resident or not and regardless of 'where' you earned it. A formula is used to calculate the proportion of salary to be taxed and this is based on the amount of time in the UK, both through work related duty and leisure.
The good news is that you're entitled to the initial tax free allowance and as such, should never end up paying any tax on the income.
BYMONEK