I think i'm right in saying that if you ask your waitress to put 15% of the total charge on the bill as a service charge, it cannot be deducted from your actual rate... The MoD picks up the tab for service, you get your full meal entitlement and the waitress gets her tip. The 10% fiasco only comes into play if service is not included on the bill and you have to cough-up "manually".
Also, we have had had a local agreement that only one person in the group need pay the bill (with a GPC card for instance). Everyone else effectively eats "free" within their allowance, and the bill payer only has to submit the names of the other non-paying diners with the bill. The free-eaters will be audited to ensure they have not claimed for the same meal.
Lots more work for us, but I feel its even more work for the few HR/Adminers that are left to audit the system.