Metal lids found at the back of building 2 mixed in with the brick and tile demolition material:
Lid marked St Martin Marmalade was manufactured by the St Martin Preservation Co Ltd. The company was formed in 1937 on the takeover of the Slough Preservation Company. In 1965 the company ceased trading and the assets sold off. Trademarks held include UK00000487089 (1937), UK~749592 (1956) and UK~749593 (1956).
Lid marked Red Heart Dog Food. In America, the Red Heart company produced a series of Base Ball Cards that were given away with their product and are now much sought after. Trade mark UK00000573000 13/11/1936 – first advert 03/02/1937.
Sources:
https://archive.org/details/
