This may be of interest, taken from page 6 of the HMRC Self Assessment Guide:
UK pensions, annuities and other state benefits received
Not all benefits are taxable. Do not include the following in boxes 8 to 13: • Attendance Allowance, lump sum Bereavement Support Payment or Personal Independence Payments • State Pension Credit, Working Tax Credit, Child Tax Credit or Universal Credit • additions to State Pensions or benefits for dependent children • income-related Employment and Support Allowance, Jobfinder’s Grant or Employment Zone payments • Maternity Allowance • War Widow’s Pension and some pensions paid to other forces dependants if the death in service was before 6 April 2005 •
pensions and other payments for disability, injury or illness due to military service • some beneficiaries’ pensions where the member
https://assets.publishing.service.go...notes-2021.pdf