I'm not sure there is any direct answer to that question. There are various factors to consider:
- The clerk is an employee and so can only claim expenses that are wholly, exclusively and necessarily in connection with their employment. This is a very strong test, and contrasts with the situation for the self employed where the word "necessarily" is not included.
- HMRC appears to allow a payment of £18 per month without the production of records. Claiming more requires detailed information about the actual costs incurred. Presumably the phrase "for each month they are required to work at home" implies that the claim must be pro rata for a part time clerk based on the worked proportion of the standard 37 hours used in pay scales.
- It is up to the council to decide whether to pay an agreed figure not exceeding £18 per month pro rata, or to require the clerk to make specific claims for actual costs.