Hi David Wylie,
Generally speaking food is not an allowable expense as it is not exclusive to your role:
BIM37920 - Wholly and exclusively: expenditure having an intrinsic duality of purpose: food and drink
However guidance on travel and subsistence can be found here:
EIM31800 - Deductions: travel expenses: general: contents
If you are entitled to the relief you can enter this under other expenses on the employment section of the return.