Germany's ultimatum to Belgium on 2 August, demanding the free passage through the country that was essential to the success of its military strategy, largely silenced the British voices that, in the 'July crisis', had argued in favour of non-intervention. The Liberal government under Asquith, which had until then been divided about how to proceed, now committed itself to conflict.

War was declared on Germany on 4 August. Three days later, the first troops from the British Expeditionary Force, under the command of Sir John French, landed on French soil. The government initially conveyed a 'business as usual' message to the British people. By sending a small expeditionary force to support France on the Continent and by using naval muscle to exert an effective trade blockade against Germany, the war would be won by Christmas. There was thus no full-scale mobilisation of Britain's resources for military conflict in 1914.

The outbreak of war radically altered the British political landscape. The issue that had dominated all others - the situation in Ireland - was suddenly pushed into the shadows. The danger of an invasion of Britain, about which the government's Committee of Imperial Defence had written numerous papers since the turn of the century, now seemed a far greater threat.

Amidst an increasingly tense and Germanophobic political atmosphere, the regulations of the Defence of the Realm Act (8 August 1914) increased the state's power to control and act against 'unpatriotic' forces. Germans and Austrians living in Britain were now categorised as 'enemy aliens' and either deported, interned or prohibited from visiting certain parts of the country. Postal and press censorship was quickly introduced.

In Britain, as elsewhere in Europe, it was assumed that the outbreak of war would prompt a wave of patriotic enthusiasm. Observing the cheering crowds in Trafalgar Square on 4 August, the philosopher and pacifist Bertrand Russell noted unhappily that 'average men and women were delighted at the prospect of war'. Many politicians and journalists repeated the truism that 'public opinion' had forced the Asquith government to declare war on Germany.

Patriotic crowds and solidarity with 'plucky little Belgium' were undoubtedly important features of the popular mood at this time. But the war also engendered a variety of other responses. It provoked resignations from the Asquith government and was vociferously opposed by left-wing organisations such as the Independent Labour Party (ILP). Even war enthusiasts such as the poet Rupert Brooke were ambivalent about a conflict that would be fought against a 'civilised' nation (Germany) and alongside a 'barbaric' one (Russia).

Outside the educated élite, many people greeted the coming of war with a mixture of determination and apprehension, rather than with any great outpouring of enthusiasm. The 'rush to the colours' after 4 August was largely ephemeral. Only in late August and early September were recruiting offices flooded with volunteers keen to enlist for military service. By the autumn, numbers were falling away rapidly.