Cattle/Club First Class travel entitlement is laid down in JSP 327. Well it was in the old one till the Brown Jobs/ Movers at Andover re wrote it (with nice purpley binder) and you can hardly find anything in it now.
It is also governed by some QR which I dont know as I have a life! However as previous people have mentioned, its now been changed to authorize at Budget holders discretion, therefore, we all go cattle class!!
If you can find an argument to justify Club/ First, then good luck to you.
If you need to get a hold of a copy, speak to a friendly, helpful ALM, or you could always ask a 'M*V*R'!