Based on the information provided I cannot see that S317 ITEPA 2003 would not apply.
The employer is providing the employee with a free or subsidised meal on the employers premises.
The legislation does not specify an exclusion against sole director (employee) employers, who's employment is based at home.
The business income manual BIM37920 advises "where food is consumed for the purpose of sustenance there will be an inevitable private purpose to the expenditure".
It also mentions "you should therefore disallow the costs of ordinary meals that serve the function of sustaining the taxpayer. It is immaterial that the physical demands of the taxpayer’s occupation require a greater consumption of food or that the location of the work place imposes a greater cost". food and drink
This ruling is a result of the case of Caillebotte v Quinn  50 TC 222.
See BIM37660 :
Wholly and exclusively