HMRC internal guidelines to tax inspectors
Where it is agreed that a worker who has previously been regarded as self-employed should now be treated as employed, then you will need to consider whether to pursue the employer for NICs and tax for back years. The law and practice relating to NICs and tax is different, so you will need to consider each separately.
ESM0117 - Employment Status Manual - HMRC internal manual - GOV.UK
Where it is agreed that a worker who has previously been regarded as self-employed should now be treated as employed, then you will need to consider whether to pursue the employer for NICs and tax for back years. The law and practice relating to NICs and tax is different, so you will need to consider each separately.
ESM0117 - Employment Status Manual - HMRC internal manual - GOV.UK
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