Muttley,

There are two Privates William McBrides entered in the Commonwealth War Graves commission register (there is also a rifleman and a 30 year old Naval Stoker).<1>

If we disregard the Rifleman and Stoker (Both no known graves, commemorated at Thiepval and Chatham respectively), we are left with:

21406 Pvt. McBRIDE, W   and 12/23965 Pvt. McBRIDE, WILLIAM both of Royal Inniskilling Fusiliers, died 10/02/1916 and 22/04/1916 respectively.
12/23965 McBride has his age given as 21, while there is no age given for 21406 McBride (neither in the record nor on the gravestone). How can you the state that THIS is the William McBride of the song? (He may have been over age and falsified his age 'backward' for all we know <2>).

The graves are both at Authuile Military Cemetary (I've seen them). From the location it is more likely that they were both killed in the
build up to the Somme campaign.

Sorry, I have insomnia and it has put me in a slightly argumentative mood tonight.

Walrus

<1> There were only 18 W. McBrides registered for the whole Great War.
<2> Yes it happened, there was an upper age for service too.