Question to the HM Treasury:

To ask Mr Chancellor of the Exchequer, what proportion of payments of (a) income tax and (b) National Insurance by employees (i) within and (ii) outside the UK were made correctly in each of the last three years.

Estimates of the proportion of payments of (a) income tax and (b) National Insurance by employees (i) within and (ii) outside the UK that were correctly made are not available.

Estimates of the value of under-declared income tax and national insurance liabilities resulting from incorrect returns are published in chapter 6 of ‘Measuring Tax Gaps 2015.’ These are produced for both small and medium enterprise (SME) employers (table 6.7) and large employers (table 6.9).

https://www.gov.uk/government/statistics/measuring-tax-gaps