Hi dimmyuk,
Based on the information you have provided, as you are potentially a non-UK tax resident in the tax year after a SRT test, you would therefore not be subject to UK NI as you had overseas employment.
If you have overseas employment you need to do a Self Assessment tax return in the future.
On your tax returns with the option to be self-employed if there is no UK employer.
If there is a UK employer, you will be subject to the PAYE processes.
If you wish to discuss this, please contact the NI helpline as below and upon your return to the UK.
National Insurance: general enquiries
Thank you.