A Bigger B.E.F in 1914 what changes?
Leaving aside the precise mechanism as to how this force develops (I know that this is a fairly major bit of hand waving), let’s say for arguments sake a combination of the poor showing in the Boer war and pessimistic concern at the results of the 1905 strategic war game the Haldane reforms generate an Expeditionary force of two Armies each with two corps (double the O.T.L August deployment). This expansion is a stretch but hopefully still within the realm of highly improbable rather than out right A.S.B. Assuming however unlikely the political will exists to fund and drive through this expansion and that the central powers don't respond to this growth in the British army with one of their own what results might this have in 1914.
Admittedly this scenario is rather sparse on detail, assume the 1st army deploys roughly as O.T.L the second army can be deployed as you wish (a product of the new Haldane reforms and war game is a continental deployment plan with a list of ships to be requisitioned and naval units committed to the plan). This is another stretch but with almost a decade to plan and build hopefully still in the realms of possibility.
1. Very little even doubled the B.E.F is smaller than French Vth army doubling the B.E.F doesn't even double the forces in Belgium, the result will be more British casualties as the B.E.F takes a bigger share of the fighting in Belgium and less strain is placed on the French Vth army with the end result that the final line stabilises roughly similarly to O.T.L.
2. A severe check to the Germans at Mons, the Belgium channel ports secured with a final line stabilising from Zeebrugge through Gent and Mons, this being about the absolute best the Entente can achieve.
3. Something in between, doubling the B.E.F adds less than 10% to the total Entente force of August 1914 and without more machine guns and motor transport in addition to numbers the likely consequence is more British and German casualties and slightly fewer French.
I apologies if this is a question that’s been done to death (I tried a search but drew a blank) or if it’s a scenario that ultimately leads only to a different western front stalemate and is as such infertile ground for interesting alt history.
I would welcome any thoughts and comments.