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.