British involvement in Russia started before the end of the First World War. In order to prevent war materials and supplies sent to Russia from falling into German hands, or being carried off without payment, a party of Royal Marines landed at Murmansk on 6 March 1918. The British force in Murmansk steadily expanded over the next few months. For similar reasons an Anglo-Japanese force landed at Vladivostok on 9 April 1918.
Two factors transformed the British position from protecting Allied supplies to active engagement with anti-Bolshevik forces: the revolt of the 70,000 strong Czechoslovak Legion against Bolshevik forces in May 1918 along the Trans-Siberian railway, and the Bolshevik government's inability (or unwillingness) to re-open the Eastern Front. By August the War Cabinet was of the opinion that any cooperation with the Bolsheviks was impossible - and if they were deposed, so much the better.
An armistice with Germany meant the Cabinet concentrated on the problems facing anti-Bolshevik forces in Russia. The decision was made to increase supplies of arms and ammunition, but not land forces. The War Cabinet's attention, although it never amounted to any action, was also directed at the states in the Caucasus and Russian Central Asia as these areas were important for India's safety.
The War Cabinet was divided over the question of intervention in Russia. David Lloyd George was in favour of only very limited intervention instead of large-scale troop deployments. Winston Churchill, on the other hand was violently anti-Bolshevik and wanted a massive British commitment. Lord Curzon, the Foreign Secretary, represented a middle ground - anti-Bolshevik but realistic, and interested in the Bolsheviks ensuring Russia would pose no future threat to the British Empire. In the War Cabinet Lloyd George's position won, despite Churchill's best efforts.
In March 1919, at the time Britain was increasing supply of munitions to White Russian Forces, the decision was taken to withdraw British forces in Murmansk and Archangel. Churchill was authorised to reinforce the garrison until the ice melted and the ports could be reopened for evacuation - he raised 8,000 volunteers from British troops waiting to be demobilised to fight in North Russia.
In October 1919 the evacuation of all British forces in the Murmansk-Archangel area was complete. The White Russian forces, although offered evacuation, remained behind and continued fighting until the general collapse of anti-Bolshevik forces in 1920. Lloyd George advocated ending supplies to White Russian armies in November 1919, signalling the end of Britain's involvement in the Russian Civil War.