So someone is supplying your enemy with preferential tariff and you would do nothing about it? They did attack US convoy when they were still neutral this is no different.
Assuming Britain is neutral then Belgium has not been invaded by either side. If Belgium is neutral, then the French army is a helpless spectator to the war and Russia must be defeated. Whether this Russian defeat constitutes a quick war followed by a moderately imposing peace, or the harsh dismemberment of the Russian Empire at the hands of an increasingly large pack of bordering jackals - that could go either way. Whether this defeat is in 1915 or 1916, this is all immaterial. The point is that Russia is going down for the count
no matter what.
Now, in the West, Britain has made a decision about the form of its neutrality. If Britain is selling both France and Germany weapons and is not interferring with German trade or naval movements, then British relations with Germany will be absolutely splendid and the tightest restrictions imaginable will be placed on German raiders and U-boats.
But if Britain is instead playing a double-game of weak intervention against Germany in the form of fake neutrality, then the situation is far more dangerous. This would come by the 2 August naval pledge to France, which amounted to a
de facto blockade of Germany whereby the Royal Navy prevents German warships their right to access the high seas, and French warships run down German trade from behind the shield so provided. British policy could enhance this weak form of hostility by passing a law forbiding direct trade or loans to any power in Europe. Then, Britain trades with France (but not Germany) via the United States. All very easy.
In the case of a double-game, make no mistake on Germany's reaction. While Russia yet breaths, the Germans will meekly accept any form of humililation and duplicitious treatment the British care to deal out. But as soon as Russia is done, then the whole of 250 or 300 German and Austrian divisions
will come at France straight through Belgium, and if Britain wants to send its tiny BEF to stand in face of that avalanche, then so be it. It would be war, and now that Britain has been foolish enough to allow Germany to dismember Russia, it will be a war on Germany's terms at Germany's leisure.