As per the DfE:
Base pay must reflect the annual salary of a member of staff as at the Census day. It should not include any additional payments or allowances. The pay of part-time or term time only staff must not be adjusted upwards to the pay of a full-time equivalent member of staff. It must also not be adjusted downwards for a member of staff that started working part way through the year. If any elements of the salary are safeguarded these must also be reflected in the base pay.