TSEM5275 - Trusts for particular purposes: employment related trusts - unfunded employer-financed retirement benefits schemes
When the employer promises to provide pension benefits but makes no contributions in advance to an unfunded retirement benefits scheme and the employer provides benefits as and when they are due, there is usually no trust.
If there is a trust it is unlikely that the trustees will have any income or gains (due to the minimal assets).The trustees do not need to complete annual returns but do have an obligation to notify any future chargeability to tax (TMA70/ Section 7).