The test of whether somebody is an employee or contractor considers factors such as who determines the hours worked, who provides the tools for the job, whether the individual may delegate or sub-contract the work, whether the individual may decide to accept or reject specific tasks, whether the individual is paid even if they do not provide a service in a particular period, whether the rate of pay is set by the employer or by the individual, whether the contract is fixed-term or open-ended etc. If more than one of these factors suggests a direct master-servant relationship, it is likely that the person is an employee. From the information you have provided, it seems clear that your lengthsman is an employee. Suggest to your Clerk that they refer to the relevant sections of the ACAS website for clarification.
There are still far too many unscrupulous employers using the old "He's not an employee, he pays his own tax" line to avoid providing sick pay, holiday pay and all the other employee benefits. Employment tribunals take a very dim view of such behaviour.