ORIGINAL: Chuck2
Every piece of official documentation labels them as regiments.
Where? Show me the map or OOB where they are marked with the regiment symbol. You can't- because they never are.
They shall be labeled as regiments. On the other hand, the infantry is usually labeled something like 3/King's Own Fish & Chips London Regiment. These we can consider battalions since there are other parts of the regiment.
More than that, they're specifically called battalions. In wartime, each regiment raises multiple battalions as the size of the army increases. In peacetime, the regiment and the battalion can be one and the same.
But there is only one 12th Field Regiment.
...and it's a battalion. The Royal Artillery as a whole is the equivalent of a regiment in the British Army system, since it has its own traditions and system of recruitment.
Think about what happens when one of your regiments is divided. One's left with a lot of "battalions". This is erroneous; the regiments break down into squadrons or batteries- because they're battalions.
You totally fail to appreciate that the British Army's regiment is totally different from the "regiment" used by, say, the US Army at the same time. The British Army retains the system that was common in the 18th century of regiments as the basis for tradition and recruitment rather than military organisation.