I don’t think reposting the picture will help me to add anything to what you already know and I add below.
For the future it looks like you’ve used a “thumbnail” of the image like is sometimes found in an album index. For any image I post I always place a full size copy on my desktop, then after clicking on “Attachments > choose file” tab below the message dialogue box, simply highlight the image on you desktop and click open. When you post your message the image will still show as a thumbnail, but when you click on it the image is displayed full size. There’s a good example on this thread I’ve answered before
http://boards.ancestry.com/topics.Military.uniform/184/mb.as... Back to your Ancestor - the differences with a Royal Garrison Artillery uniform to the other branches, is that Garrison artillerymen carried swagger sticks and were issued trousers and boots, rather than carrying a whip and wearing breaches and riding boots as issued to Royal Field & Horse Artillery troops.
Looking at the image again I should have realised what he is holding is more likely to be a swagger stick than a whip and he could be wearing trousers rather than breaches, so although I would have preferred the picture to have included below his knees before stating the artillery branch he served with, it does look like he was perhaps serving with the Royal Garrison Artillery at that time.
A couple of things about his service in WWI, although the uniform was typical until 1902, and a little later for some part-time Militia and Volunteer units, be aware he may not have been serving with the RGA in WWI. If he was a regular soldier serving in 1902 it’s possible he was discharged by 1914, so may have served with a different regiment.
If he died in 1918 of a cause associated with his WWI service, even if discharged earlier, he should be recorded as an official WWI casualty on the CWGC site at
http://www.cwgc.org/. Even using the advance search, I couldn’t see anyone named Alfred Webb who died in England in 1919 (casualties counted up to Aug 1921) that was likely to be him.
He wouldn’t be the first to have been omitted from there records, many names have been added since the end of the war, the key is providing full supporting evidence of your Great Grandfather; that should where possible include his reason for discharge matching what appears on his death certificate; circumstantial evidence is rarely successful.
I assume his death is recorded in the GRO Index to Civil Deaths registered reference:
Webb, Alfred, Sept Qtr, 1919, age 42, District West Ham, volume 4a, page 149.
If you don’t already have access to a copy, one can be obtained using the above reference via
http://www.gro.gov.uk/gro/content/ Also check for an obituary in a local West Ham newspaper of the time; if one exists it will probably mention the unit he was discharged from.
Next you will need have some real luck, you need to check for a service or pension file (all that survive have been digitised and placed on Ancestry), but you are hampered in that you don’t appear to have any data to base any search on.
If he served overseas he will have a medal index card, if he was stationed at home he would not have a card for WWI Campaign Medals, but could have still been injured or become sick while on war service, e.g. one man I know of contracted TB during training, was discharged and died of it later; he’s been included as a war casualty.
A check of the catalogued Medal Index Cards at the National Archives web site shows there are 223 cards for soldiers named Alfred Webb and a further 47 for the name Fred Webb; of those 28 Alfreds and 5 Freds served with some branch of Artillery. Aged 42 in 1919, even if he did serve with the artillery during WWI, it’s possible he served with the Labour Corps before discharge so cross check for both regiments on MICs.
If he was discharged through wounds or illness during his military service, he should have been granted a Silver War Badge and although they will have an MIC, you should find the number of possible names significantly reduced by searching the SWB Lists that are also on Ancestry.
If you do find some record showing he was discharged from the army for the same reason and his cause of death, contact the In From the Cold Project at
http://www.infromthecold.org/ for assistance in getting Alfred properly commemorated.
Good Luck