Your residence status decides it, not the move itself
You are taxed in the UK on your worldwide income for as long as you are UK tax resident, and residence is decided by the Statutory Residence Test, not by booking a one-way flight. The test weighs your UK days and ties across the whole tax year (6 April to 5 April), so a mid-year move to Spain usually needs split-year treatment to draw the line: HMRC then taxes you as resident only for the UK part of the year, and income arising in Spain after the split date is broadly outside UK income tax.
The trap: UK-source income does not switch off
Becoming non-resident does not end UK tax on income with a UK source. Rent from a UK property stays UK-taxable however long you live in Spain: register under the Non-resident Landlord Scheme (form NRL1) to receive the rent gross, then report the profit to HMRC. If you sell UK residential property while non-resident, you must file a Non-Resident Capital Gains Tax return within 60 days of completion, even when no tax is due. If your non-residence lasts five years or less before you return, gains realised while abroad can be pulled back into UK tax under the temporary non-residence rules.
What to do before you go
Pin down your leaving date against the SRT, confirm which split-year case applies, decide what happens to UK property and pensions, and file the P85. Under the UK-Spain double tax treaty, UK private and state pensions generally become taxable only in Spain once you are resident there, while government-service pensions stay taxable in the UK, so treaty relief claims are often needed to get tax deducted in the right country. On the Spanish side, weigh normal residence against the Beckham Law regime, which must be applied for within six months of registering for Spanish social security. Our full guide to moving to Spain from the UK walks through the whole sequence.