The old Metropolitan/GWR tie-up used steam locomotives through Paddington, before EMUs became the norm. The Bo-Bo's, as modelled by Heljan, dated from 1920/21, and were used almost exclusively between Baker Street and Rickmansworth, where they were removed from their trains and steam locomotives took the train onwards to Amersham or even Aylesbury in early days. After electrification to Amersham in 1960, the A60 stock took over services all the way from Baker Street to Amersham and Chesham, and the Bo-Bo's were retired, with a couple being preserved. The LT lines onwards to Aylesbury were transferred out of LT hands somewhat earlier than this.
No 12, Sarah Siddons was for a while officially the brake block test locomotive, a neat way to preserve a locomotive in operational condition without actually "officially" preserving it!
The Heljan model is superb, and as we expect from this manufacturer, they run very quietly and smoothly, and have more than enough power to haul any stock we would deem suitable - mine are only expected to haul five lightweight coaches (Graham Farish non-gangwayed coaches painted brown).
I bought one at full price when they first arrived (No. 8 Sherlock Holmes), but like the OP, I succumbed t temptation when the bargain priced ones appeared for £74, so bought No 12 Sarah Siddons in preserved Met livery as well.

IMG_20180603_100436 by Jeffrey Lynn, on Flickr
As a small aside, both of mine had the same minor fault, where the lighting boards for the top marker light and cab light were inserted upside down (both ends of No 8 and one end only of No 12); this was very easily fixed!
No 12, Sarah Siddons was for a while officially the brake block test locomotive, a neat way to preserve a locomotive in operational condition without actually "officially" preserving it!
The Heljan model is superb, and as we expect from this manufacturer, they run very quietly and smoothly, and have more than enough power to haul any stock we would deem suitable - mine are only expected to haul five lightweight coaches (Graham Farish non-gangwayed coaches painted brown).
I bought one at full price when they first arrived (No. 8 Sherlock Holmes), but like the OP, I succumbed t temptation when the bargain priced ones appeared for £74, so bought No 12 Sarah Siddons in preserved Met livery as well.

IMG_20180603_100436 by Jeffrey Lynn, on Flickr
As a small aside, both of mine had the same minor fault, where the lighting boards for the top marker light and cab light were inserted upside down (both ends of No 8 and one end only of No 12); this was very easily fixed!