Hi Clive
I have only just seen your post but fortunately I can tell you everything about your ST paperweight. If you look at a map of Cornwall, about 7 miles from Wadebridge (just off the A39) is the small village of St Tudy. There lived a couple named Bernard and Dorothy Broughton who had built up a large collection of paperweights and they would open their house and allow people to come in and view their weights. This proved a popular attraction so in the 1970's the Broughton's asked Liskeard Glass to make a selection of paperweights with ST impressed in the base for ST TUDY and they sold these to their visitors. I had one with a piece of Cornish Granite encased inside over a blue swirl base and another multi facetted weight containing Murano Canes as shown in picture attached
The Broughton's sold their collection in the late 70's or very early 80's and the new owner moved this to a place called Leg 'O Mutton near Yelverton and opened The Yelverton Paperweight Centre and, following the Broughton's lead, they asked Liskeard Glass to make weights with the letter Y impressed in the base. Basically these were the same designs as the St Tudy ST weights. The Yelverton Paperweight Centre sadly closed some ten years ago
Hope this answers your question Clive
Dave