'quasi' self employed daily subsistence rates and per diems film industry guidance

A self employed person working in the film industry. They qualify and meet the criteria of as a self employed grade person within the film industry. As is usual, even though they are self employed they have a contract with the film production company, Part of the weekly payslip will have a separate line for income as a 'per diem'. The film production company pay this per diem as a standard weekly amount and is I would presume a set amount agreed within the guidelines of HMRC per diem rates. The per diem is part of income and will be subject to VAT. The self employed person meets the qualifying conditions for a person travelling. My question is, can the self employed person claim the per diem, being a reasonable amount, as a subsistence expense instead of claiming for actual receipts spent on food/drink. This query I believe needs specialist knowledge of the legislation and agreements with HMRC and the film industry and I would like guidance from an experienced advisor working specifically with individuals working in this industry as I don't believe it is a 'normal' situation of a self employed person. And any case law around this would also be welcome.

Hi Don Corleone,
Please contact the Film Industry Helpline on 0300 123 2326, for matters of this nature.
Thank you. 

Hi Don, I wonder if any specific guidance was relayed to you from the Film Helpline? We work with hundreds of actors, many of whom work abroad and are paid in a similar way, which I also assume is an amount calculated using the HMRC Scale Rates. Look forward to hearing from you.