The Mid Wales Hospital, Talgarth, Brecknockshire was originally called the Brecon and Radnor Joint Asylum on opening in 1903; the name was changed to The Mid Wales Hospital in 1921.
The local archives will be your best bet. Most institutions records are passed onto the local authorities for exactly your sort of enquiry. Good luck!
Is there any way to access archive material relating to a patient, my grandfather, who was institutionalised in Talgarth after being evacuated from France in 1940. I am interested in the years 1940 – 43.
Is there a register(s) of former residents at the hospital (I’m looking at the period 1903 to 1939)?
Yes there is, it’s part of the planned future use as a wedding and conference centre if rumours be true. Who owns the site? Nobody really knows.
Is there a church on the site of the Mid Wales Asylum area?