Hi,
Box 36 Adjustment to payments on account for capital gains. If you have put an amount in box 35, a nomination for capital gains, put the amount of Capital Gains Tax included in either the £30,000 or £60,000 RBC in box 36. If you are working out your own tax, do not include the amount shown in box 36 in your payments on account calculation. You can see guidance here:
Residence, remittance basis etc notes
Thank you.