HMRC have published detailed guidance relating to employers operating PAYE in real time with expatriate employees working either in the UK or overseas.
Part of this guidance reads as follows:
"HMRC will apply a common sense approach to deciding whether we agree that employers of expatriates have a reasonable excuse for not telling us on time about any tax and NICs due on payments and notional payments made in-year to expatriates by third parties and overseas employers; or for not paying this tax and NICs by its due date. In assessing whether we agree that employers have a reasonable excuse, HMRC is not expecting employers to materially change the operation of their current UK or overseas payrolls for making payments to employees where these payroll practices are reasonable and widely accepted."
The full guidance notes can be accessed here.