Not much to go on, but the light coloured stripe under the lower deck windows doesn't match most Tillings companies.
If it is Wales, some of the municipal operators ran inter-urban services, so could have been somewhere this rural, or it could have been a company operator or possibly even an independent.
The bus could just be from before 1939, or not long after. Or possibly a wartime 'utility' along the lines of
this Daimler (not my photo) - the radiator looks as if it could be Daimler shaped, but I'm not certain.
By 'feel' alone, I'd say the photo's probably from not that long after the end of the 1939-45 war, but again, I'm not at all certain.