In the days leading up to the outbreak of war the issue of Belgian neutrality came to the fore. On 2 August Germany requested free passage through Belgium in order to rapidly move against France. This was refused and the following day German troops crossed the Belgian border.
At that point there was no majority amongst members of the British cabinet for declaring war on Germany, even if France was attacked. However, whilst the Entente Cordiale signed with France in 1904 did not constitute an alliance a treaty of 1839 did bind Britain to guarantee Belgian neutrality.
This is a note made by David Lloyd George (1863–1945), then Chancellor of the Exchequer, and Winston Churchill,(1874–1965), then First Lord of the Admiralty, at a Cabinet meeting the day before Germany's request to Belgium.