The Didcot Newbury and Southampton Railway was absorbed into the GWR at the grouping of 1923 but the LSWR (and later SR/BR-S) worked and maintained the 2 miles 6 ch. between Shawford Junction and Winchester(DN&S) under an 1890 agreement.
Control of single lines by tablet was the standard LSWR practice, although GWR staffs and key tokens were used on the single line sections of the DN&S line north of Winchester.
Ref. "The Didcot, Newbury & Southampton Railway" by T.B. Sands, Oakwood Press.