Sounds like a load of nonsense to me, given that valves haven't been made at Blackburn for at least 24 years.
When they were made there, they were made on a huge scale, on plant that isn't there any more, by people who are mostly gone (the grey haired guy at the front would have been a pretty junior employee back then, or at school), and using processes which wouldn't get through modern environmental specs (ISO14001 anyone?) without massive investment.
Call me cynical, but it's just cashing in on the tiny flake of heritage they've found themselves clutching.