Frank thank you, I was hoping you'd see this topic and comment. I've been digging and found some bits which are on Simba's other topic re the wine sets in British and Irish Glass here:
http://www.glassmessages.com/index.php/topic,59518.0.html but for ease of reference I'll add what I found here too...
I've just found entries for the company in the PO Directories for Glasgow dated between 1926-28:
West George street. 37 . Wright & Pouncy The Denholm Manufacturing Co., Ltd who are listed as clock manufacturers and importers
and an undated entry also in the PO Directory for Glasgow:
The Post-Office Annual Glasgow Directory
The Denholm Manufacturing Co., Ltd., clock manufacturers and importers, Morrison court, 108
Argyle St., C.2
And a wee bit more... The Denholm Manufacturing Company Ltd went into voluntary liquidation in 1932 and was finally wound up in 1933 [Source: London Gazette, 8th April 1932 and 24 March 1933] so that gives us an end date for them!
Or maybe not..

... as a search of the National Archives gives the following result:
Reference: BT 31/32646/200510
Description: No. of Company: 200510; Denholm Manufacturing Company Limited. Incorporated in 1924. Dissolved in 1948.
So they appeared to have been a short-lived company... unless someone knows better!