Yes, all British soldiers were paid during the First and Second World Wars. During the First World War, British privates in the infantry were paid 1 shilling a day, I'm not British and I can't find a good converter so I can't tell you how much that actually converts to in today's currency. The rate of pay varied per arm of the military and of course the higher your rank, the more you got paid, a Lieutenant Colonel in the infantry for example was paid 28 shillings a day. This website has a good list of the pay rates of the British army during the First World War

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