The Melton Works in Capper Pass, Humberside, operated from 1937 to 1991 and was a major producer of tin and an important industrial employer in Humberside.
In the early 1990s, as a young contaminated land consultant, I carried out a ground investigation at the site post-closure and a security guard gave me the ingots as a memento. They were lying amongst the rubble of the former works and were a poignant reminder of what had been on the site before and the thousands of people that had worked there.
The larger of the two tin ingots in the photograph weighs 2.5kg and is 'standard' tin. The smaller one was produced during a one-off commemorative operation and is an order of magnitude purer (99.999% pure I believe). It weighs 150g and I was told that very few were made.