Service records available from the Ministry of Defence Veterans Agency
If the soldier continued in service to 1921 or later (and the possibility of his re-enlisting in 1919 for just one or a few years service should not be ignored: thousands did so) or if he returned to serve in the army in WW2, his record will not yet be public. It can be obtained – on payment of a fee and demonstration of evidence of kinship – from the Veteran’s Agency: link to their website
In 2014, the Ministry of Defence released under a Freedom of Information Act request an index to the records that they still hold of men with dates of birth before 1901: link to index
But what will you receive? It depends on your status as an applicant.
Restrictions on data that will be released
This information is based on a letter being issued by the Army Personnel Centre to applicants in 2020: