I understand that if someone gets a reduced rate mortgage from their employer then the interest difference will be reported as a benefit in kind, which will then impact on the personal allowance the following tax year by reducing the tax code.
Does that then also impact the NI contribution?
e.g. personal allowance £6475, interest difference to official rate, say, £1,200. Remaining allowance £5275. So tax code will be 527 instead of 647, so does that lowering of the tax code impact on NI, or is it calculated on basic salary regardless of tax ?