Hi Annie-Lee Cox,
You can either refund actual costs or use a benchmark rate, you can't use both methods on a single transaction type.
So as you are already using a benchmark rate for subsistence, yes the food element of these vouchers woud already be covered by that and would therefore not also be reimbursed as actual costs.
Exactly how you determine that is not something we can advise on.
You may also wish to consider depending on your circumstances the industry scale rate for lorry drivers overnight subsistence.
Please see EIM66205 for further information:
EIM66205 - Tax treatment of lorry drivers: employer guidance: scale rate payments to drivers
For VAT related questions you would need to contact VAT helpline.
Please see here for contact details:
VAT: general enquiries
Thank you.