I'm just about to begin this process myself and am most interested in the war diaries, though I think I might need the service records first, to obtain all the appropriate unit numbers etc. Or can you obtain regimental records without these details?
Of the three places that the diaries are held, how do you know which will hold yours? Or are there 3 copies of the diaries, with one in each of the places above?
I think I found the answer to this fro the WDYTYA website:
All Army Units kept a War Diary, recording their daily activities, invaluable for finding records of movements, training and fighting a relative took part in. Diaries are at TNA, held by ‘theatre’. If a unit served in France in 1939, then in Britain after Dunkirk, later in North Africa and in France after D-Day, you’ll have to search several theatres to get the whole history. Diaries may include maps, orders, intelligence, lists of men attached from other units or away on detachment and notes on operations.
Unlike First World War War Diaries, some of which are online, all those for the Second World War still have to be viewed as original documents at TNA. By diligently following the diaries, it’s possible to build a good picture of your relative’s career.
To help you search for a particular diary there’s a list of war theatres in TNA’s online research guide entitled ‘Second World War: British Army Operations 1939-1945’ at
www.nationalarchives.gov.uk/catalogue/rdleaflet.asp?sLeafletID=161. Service records and War Diaries provide a firm foundation for your research and suggest avenues to investigate your Second World War Army ancestors further. The discoveries, and hard work, have only begun!