Gross Pay Vs. Taxable pay implications

My gross pay will be over £50'000 this current tax year, whereas my taxable pay will be under £50'000. This is due to car mileage I am paid as part of my job. The difference is around £5000 and it will only be for this tax year due to me receiving a lump sum back payment. Next tax year I anticipate my gross pay will be below £50'000. For the purposes of interest on savings and child tax credits will I qualify as a higher rate tax payer for this tax year? Will the amount that appears on my P60 at the end of the tax year be how my tax status is calculated? many thanks

Hi,

It will be based on the taxable pay figure.

Thank you.