You should contact The National Archives (former Public Records Office) at Kew Gardens in the UK. Go to their website first, it is very good to orient you with that large institution, which is very reader friendly, unlike many other archives.
TNA has large holdings of WW1 soldier records and efforts have been made to make them accessible. With enough details, you could hire a TNA-approved researcher to find and make copies. Or better still, go there yourself. The website has a list of the B&Bs in the area. Book ahead and be sure to book one in Kew, not in Richmond. From Heathrow Airport, one can get to Kew by the Underground by changing lines at Hammersworth and take the Disrict Line underground to Richmond. Kew Gardens is one stop before that. Or take a taxi but that will be about 25 quids.
Good luck and have fun!
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