EIM43030 | Employees resident in the Irish Republic: claims to exemption from United Kingdom tax
From HM Revenue & Customs · Employment Income Manual
A claim to exemption from United Kingdom tax in respect of an employment should be accepted only where all the following conditions apply (see DT220):
the time spent in the United Kingdom during the tax year does not exceed 183 days in total
the remuneration is paid by, or on behalf of, an employer not resident in the United Kingdom
the remuneration is not borne by a permanent establishment (or a fixed base) which the employer has in the United Kingdom.