As usual, I agree with Wiking.
To the rather far-fetched idea that Britain would declare war on France, rather than simply finding ourselves stuck:
never overestimate my country's commitment to treaty obligations.

Seriously, we invaded Greece and overthrew their government just like that. We weren't playing international policeman, we were playing the same great-power game as everybody else.
And why does everybody always bring up Japan? Japan had a binding alliance with Britain, and what's more they did well out of the war, using the distraction of the European economies and diplomacy to expand their markets and expand their influence in China. What do they get from jeopardising their most important relationship and marching into MMBS (Miles and Miles of Bloody Siberia, as it is technically known by cartographers)?
So, suppose the Kaiser had known this and forced von Moltke to comply or resign?
I'd note that this kind of PoD ("X historical figure had knowledge nobody could have had at the time") necessarily makes this a hypothetical. Nothing wrong with hypotheticals, but I object to the serious use of such PoDs, which you see rather a lot.
(German troops threatening the Channel ports was a determining issue as far as I've understood).
That's simplifying a great deal. British strategic policy
had moved on from the sailing age (the admiralty had officially ceased to be bothered about the Turkish Straits in 1903, for instance), and in the steam age (the age in which a fleet can reliable sail out and intercept another one) it's not the proximity of the ports that matters as much as the ability of a rival industrial power to build a mighty fleet. Germany was a threat in a way that France could no longer be, and Belgium was something in the nature of a pretext.
Without Belgium, Britain might well enter the war later, with more controversy within the cabinet; that depends on how the war goes. But certainly we will be more-or-less friendly to the Entente.
The German strategy was based, in fact, on the idea that since they were challenging our vital interests anyway, they might as well go all the way.
So suppose now it's spring 1916 - Britain is still neutral, as is Italy (not so eager to join the entente without Britain), half a dozen great French offensives against Alsace Lorraine have smashed themselves to pieces against the German trenches, and Russia is reeling on the brink of total defeat, it's western front collapsing and the Turks swarming all over the Caucaus.
Now, this is the bit of the premise I doubt. We have a really caricature picture of some aspects of the war, so:
1) The western front in 1914 was a damn near thing, and that was with approximately equal forces. Taking four German armies away is going to put the Germans in a tricky situation, even if they are standing on the defensive. The French
did make gains in Alsace in 1914, and that was with considerable forces and reserves tied up in the battle that developed from the Belgian thrust. The full French army against about the same German forces in Alsace and Lorraine?
Remember, every step the French advance is cutting into one of Germany's plum industrial zones. The Germans, meanwhile, have not captured the enormously important industrial agglomeration of Wallonia, nor Brie, the loss of which crippled French production. The French are couple of million military-age males and one-and-a-half of Europe's prime industrial zones in the black; the Germans have lost Wallonia, they've lost Brie, and they're on the back foot in Alsace.
The French are going to bleed something awful, but this is
not a one-sided contest.
2) So the Germans deploy much greater forces in Russia and adopt an attacking strategy? This presumably means that the ammunition crunch comes along earlier and the Russians have to start abandoning Galicia and their bit of Poland earlier - and then what? It didn't stop them in 1915. They'll do what they did IOTL: keep withdrawing and keep mobilising larger and larger armies until their social structure finally gives out. If you asked the tsar in late 1916, Russia wasn't losing. Russia didn't suffer "total defeat", it suffered implosion.
And is that collapse going to come any earlier? Much of Russia's appalling casualties were the fault of repeated rash offensives. Forced onto the defensive, Russia may actually be making better use of its own manpower. You can't force a decisive battle on a country the size of Russia; in that much German strategy was sound.
I think the French would only pull such a stunt if they had sounded us out first, and given our probably response, I think the French wouldn't pull such a stunt.