I know the Canadians maintain reserve depot regiments of around a company size each, but the UK does not do this because they are not what we need. As Neutralizer points out we will simply add new battalions to existing regiments if and when they are required. Its a very practical solution that gives the army what it requires. I reckon that if each current regiment had 30 battalions, the army would have over 400 in total - enough for over 40 infantry divisions! In any case regiments remember and pay respect to their lineages.