I was under the impression that all who joined the Imperial Yeomanry were classed as volunteers, but apparently not in the eyes of UK law. This case, brought by William Blake, got wide coverage around the country in provincial newspapers.
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"In the King's Bench yesterday the hearing was concluded of the case of Blake v. Hitchcock, Williams, and Co., drapers, St. Paul's-churchyard, London. The plaintiff, formerly a warehouseman employed by the defendants, sued to recover fully £100 due to him as the balance of salary under an agreement. The plaintiff's case was that in December, 1899, he volunteered for South Africa after the defendants had given notice that all employees of theirs who volunteered would have places found for them on their return, and would be given their salaries while at the front. The defence was that the offer only applied to employees who were already volunteers, and that there was no special agreement with the plaintiff. Mr Justice Ridley held that there was no evidence of contract as relied on by the plaintiff to go to the jury, and entered judgment for the defendants, with costs. Stay of execution was granted, in view of an appeal."
Aberdeen Daily Journal, Thursday 10th April 1902
"In the Court of Appeal on Thursday the case of Blake v. Hitchcock, Williams, and Co., drapers, St. Paul's-churchyard, was heard. At the trial plaintiff contended that defendants were under a contract to him to keep his place open in their establishment and to pay him his salary during his absence in South Africa with the Imperial Yeomanry. Defendants alleged that the undertaking did not apply to defendant, as he was not a volunteer. Justice Ridley took this view, and the Appeal Court upheld his decision."
Cheltenham Chronicle, Saturday 1st November 1902