Why the claim can fail after you made it
Case 1 split-year treatment is not banked on the day you fly out. It requires you to meet the SRT's sufficient hours overseas test for the relevant period running to the following 5 April, with UK days and UK workdays within the statutory limits throughout. The same structure applies to full non-resident years: the third automatic overseas test asks whether, across the whole tax year, you worked sufficient hours overseas with no significant break, spent fewer than 91 days in the UK and had fewer than 31 UK workdays. HMRC defines a significant break precisely: at least 31 days pass and none of them is a day of more than 3 hours of overseas work, or a day you would have worked but for annual, sick or parenting leave. A redundancy or early contract end starts that clock immediately.
The 31-day window, and the fallbacks if you miss it
If you take a new overseas role before 31 days elapse and stay within the day counts, the full-time work conditions can remain satisfied and the split year stands. If the gap runs longer, Case 1 fails for the year, but that is not necessarily the end of the split. Case 3 splits the year from the day you cease to have any home in the UK, provided you spend fewer than 16 days in the UK after that point and, within six months, become tax resident in or establish a sufficient connection with the country you moved to. For later years, non-residence can also rest on the day-count tests and the sufficient ties test under the Statutory Residence Test rather than on full-time work. Which route holds depends on your homes, your days and your calendar, so the analysis has to be rerun against what actually happened.
Fixing the return, and the five-year trap
Because the conditions run to 5 April, a return filed claiming Case 1 before the year was secure has to reflect the position that actually held by the year end; if the conditions failed, the year is taxed on the basis that truly applied, and leaving a failed claim uncorrected invites penalties on top of the tax. And if the job ending brings you back to the UK, remember the temporary non-residence rules: return within five years and gains and certain income realised while you were abroad can be taxed in your year of return. Horizon UK Tax Solutions reruns the SRT and split-year analysis after a change of plans and corrects the filings on a fixed fee agreed upfront; book a free 30-minute clarity call as soon as the job ends, while the 31-day window is still open.