London Underground gets an airing on this forum from time to time but Hornby still don;t seem keen on making one.
A local cheap shop (you know the sort, narrow aisles piled high with discounted and bankrupt stock) was selling Underground Ernie rolling stock a few years ago, so I succumbed and bought one of each, more out of curiosity than anything else, all at a fraction of original prices.
I tend to buy up Underground stuff whenever I see it, I already have a 7 car ERTL 1938 tube train, unmotorised, three Heljan Metropolitan Bo-Bos, two Bachmann 57xx in LT Maroon, a handful of wagons in LT livery and one of those Ever-Ready three rail tube trainsets, sadly with a seized motor. I also have a single coach of a diecast tube train painted in red. white and blue livery which was sold as a souvenir in London.
I certainly would buy and run London Underground stuff if it was available although my preference is for the stuff before 1968, but I fear there is little enthusiasm for it.