Personal Tax Return Client (not self employed) - can my fee be entered as an expense in their tax return?

I'm preparing a tax return for a private individual who is paid by PAYE and has no self employment income, property income, etc.  Other than a bit of interest the only income is his PAYE income.

My head tells me that surely he can claim my fee as an expense in the same way that one would recover, say, a subscription to a professional body (that wasn't paid by the employer).  However the only place it would make sense to put this is in box 17 in the Other UK Income section of the self assessment.  The guidance would seem to suggest that this isn't an allowable expense though.  On that basis I was going to exclude it, but this seems a little unfair so wanted to check.

Can my fee be included as an expense or not?

Thanks in advance