DS
I have had cause to investigate the entitlements and can confirm that the allowance does indeed appear to be £21 for on or two meals and drinks, without splitting it out - although the 'abated' rate is something like £4.20 and this is supposed to cover your 'minor' meal of the day - ie lunch when the MOD provides dinner.
What is more interesting is that it now seems acceptable to claim for an alcoholic drink (one 'reasonable' one only!) - I have actually had SP Pol confirmation of this!