Hi R A
On SA100, page TR4, box 1 relates to payments to a pension scheme, after tax has been deducted from their salary.
20 percent tax relief is automatically given when the payment is made to the pension scheme, so higher rate taxpayers can claim a further 20 percent tax relief by completing this box.
Box 2 is for payments to a pension scheme, after tax is deducted from the salary and no tax relief has been given.
This box allows an individual to claim 40 percent tax relief if higher rate and 45 percent if additional tax rate is paid.
Box 3 is for payments to an employer pension scheme made, after tax was deducted from the salary and box 4 is for payment to a foreign pension scheme.
If an individual pays into a pension scheme before tax is calculated from their salary, then full relief is given at source and no further relief is due.
Guidance for the SA100 (2023) tax return can be found here
Tax Return notes
Thank you