Neil.
Jim Nunn of Crawley built a 5" LMS Garrett in the early 70s. I last saw it at Gilling seven or eight years ago. There was a 7 1/4" LNER Garrett at Harrogate last year. Brand new, very impressive and kind of hard to miss. The late Geoff Gregson of Urmston built an East African Garrett in 5" gauge during the eighties whilst he was living near Sunderalnd. It ran in IMLEC a couple of times with Geoff's son Nigel at the controls. Brian Hollingsworth (who wrote LBSC His Life and Locomotives) owned one of two or three African Garretts that appeared in the mid seventies. They were I think 7 1/4" but were very big being of narrow gauge prototypes. I first saw Brian's Mount Kilimanjaro on exhibition at Shildon for the 1975 S&D 150.
The full size LMS Garretts were build for coal haulage to London and were concentrated at Toton I believe. I know they sometimes worked into York in the fifties.
I would be surprised if these were the only model Garretts to run here and I'm sure there will be more information from other members to follow.
Eddie