Residence decides who taxes your salary
Nothing in UK tax law stops you being employed by a UK company while living abroad; what changes is who gets to tax the pay. Start with the Statutory Residence Test. If you go for a few months and stay UK resident, UK PAYE carries on and the treaty usually protects you from host-country tax. If you genuinely move, become non-resident and do all your work abroad, the taxing rights shift to your new country. Beware the 183-day myth in both directions: being out of the UK for 183 days does not make you automatically non-resident, and staying under 183 days in the host country only avoids tax there if all three treaty conditions are met, including that your pay is not borne by a permanent establishment your employer has there.
The sequence: P85, NT code, split year
There is an order to getting the UK side right. First, tell HMRC you have left: the online P85 after departure, or, if you are filing a Self Assessment return for the departure year, the return with its residence pages does the same job, and GOV.UK says not to do both. Second, once non-residence and wholly overseas duties are clear, HMRC can issue the NT code; it is normally operated cumulatively, so when it lands the payroll automatically refunds tax over-deducted since you left. Third, the departure year itself: by default you are UK resident for the whole tax year you leave, but split-year treatment under Case 1, starting full-time work overseas, can split the year at your departure date so overseas-duty earnings after that fall outside UK tax. Until all this is settled, PAYE money is delayed, not lost.
National Insurance is a separate question
An NT code stops tax, not National Insurance. In the EU, Gibraltar, Iceland, Liechtenstein, Norway and Switzerland, and in agreement countries such as the USA, Canada and Japan, certificates of coverage decide which system you pay into. In non-agreement countries the 52-week rule can keep you and your employer paying UK Class 1 NI for the first year abroad if the move is temporary and the other conditions are met, sometimes alongside local social charges. Once compulsory NI stops, consider voluntary contributions from abroad to protect your State Pension, noting that from 2026/27 only Class 3 is available for new periods abroad. Your employer has its own list too: section 690 notifications for mixed UK and overseas duties, host-country payroll and permanent establishment risk. Horizon coordinates the P85, NT code, treaty position and departure-year return on fixed fees agreed upfront; book a free clarity call at /book before you fly.