Workplace private pension
Scheme administrator or employer HR; provide death certificate and any expression of wish
Some steps differ by region inside the country.
Where
Each scheme administrator, the employer's HR for older schemes, and the Pension Tracing Service for anything you cannot find.
How
List every employer they ever had, then contact each scheme, not just the most recent one.
Use the Pension Tracing Service for schemes whose administrator you cannot identify.
Ask each scheme about death benefits, dependant pensions, and whether an expression of wish form is on file.
Provide details of all dependants, since trustees usually exercise discretion based on dependency.
What to bring
A certified copy of the death certificate
Their National Insurance number
Scheme or member numbers
Details of dependants and any expression of wish form
Timing
Often 3 to 12 months, because trustees must identify and consider all potential beneficiaries.
This is practical information, not legal, medical, or financial advice.