Green’s Dictionary of Slang

a blade that does not cut.

1902-04

V.S. Lean Collectanea I 138: A Leadenhall blade. One that will not cut.

a ‘bag’ fox, released when a hunt cannot find any wild foxes; they were sold at London’s Leadenhall market.

1860		R.S. Surtees Plain or Ringlets? (1926) 149: Will Ranger, the inder keeper’s voice, who has jyst shook a bag fox, a regular leadenhall gentleman.
1877		Cheshire Obs. 10 Mar. 7/4: A certain pack of Cheshire harriers have been enjoying rare sport with a bagman. This Leadenhall gentleman has been twice taken alive after two good runs, and it is expected that he will give them one or two more.
2019		hidden-london.com 🌐 A ‘Leadenhaller’ was an alternative name for a ‘bagman’, who sold live foxes in bags. They were [...] brought in (mainly from France) to overcome the scarcity created by the destruction of the animals by gamekeepers and farmers.