Given that Establishments were notified in ACIs, then if you want a comprehensive list then the first place to look is in ACIs. That said some ACIs may have been highly classified and used to notify highly classified Establishments, but these should all be in TNAs ACI series. There are other sources that listed new or revised Establishments, for example the monthly RA Notes that started in Jan 43 usually notified changes in at least some RA establishments. I'm happy to report that having an interest limited to a particularly large branch of the army, field unit establishments and post 1940 only, I've never had any need to go beyond WO 24/950, 951 so don't be put of by tales of umpty ump volumes, for most researchers it is not a problem. Of course it helps if you know what you are looking for. All the training establishments, base depots and organisations and the like are irrelevant to the field Order of Battle, depending on your criteria so too were the AA regts in AA Command UK, given that a significant proportion of HAA regts were each on different Establishments you can see why its useful to be clear on your area of interest! There are other ORBAT sources, for example WO 212/3 covers "Order of Battle for the Field Forces in the United Kingdom Part 2 Armoured Divisions and Royal Armoured Corps Series 3 Number 5 amended up to 14 Sep 42", and a further amendment to it. This lists all units, together with what I assume is their Unique Identification number, for example 9 Armd Div supply & transport comprised HQ 9 Armd Div RASC, 28 Armd Bde Coy, 7 Inf Bde Coy and 9 Armd Div Tps Coy. All the unit LADs are listed separately. WO 212/15 deals with infantry, etc divisions and bdes for the same period in UK. The next series of interest in WO 73, 'Strength of The British Army and of Other Military Forces in British Commands", these are quarterly statements. Those in the first half of the war provide the War Establishment number for each unit, the Estb strength and the actual strength, the later ones just give actual strength, the early ones are useful for identifying which is the relevant Establishment at reporting date. Note that these are organised by regiments and corps in theatres. Interestingly they also give the current number of PoW and Internees, for example for June 44 there were 1005 RA officers and 16403 ORs whereas 12 months earlier there were 1042 Offrs and 14712 ORs (updated ICRC info for those held by Japan?). Now, where are the AFG 1098 in TNA? I should also caution about Sheldrake's warning. He is clearly young and does not realise that the British Army changed it stores accounting arrangements in about 1968. The 'modern' accounting system is as he says, before that it was a lot simpler and generally units had what it said in the AFG 1098 (it helped that the equipment was a lot simpler and versions tended to last for longer because there was less of the 'this year's version' from industry).