Heavy braking is of course much more likely going downhill.
How does it work in a Garrett? Is there a single live steam feed at one end of the boiler serving both pairs of cylinders? A Double Fairlie must be a difficult proposition as it is impossible for both chimneys to be at the uphill end!
(Garrets were once a common sight on the Midland Main Line, but I doubt any of them was ever seen at Liverpool Street, let alone Chingford!)
Single feed from the dome to a junction box which feeds both units equally (theoretically!) until one end picks its feet up and then the force causes the steam supply to head off in one direction more than the other! They occasionally do prime, but it is quite rare, even with the water out of sight at the top by quite a margin.
Fairlies are just a slight odd-ball in the way they function. I've had the pleasure a couple of times of driving them on the Welsh Highland and they seem to take it in their stride. You do have to hold your nerve on the water front mind you.
And finally...it's GarrAtt, a GarrEtt is a traction engine!
Garrets were .............Used I think for coal trains between Nottingham collieries and Cricklewood?
Exactly so. The LNER also had a Garrett, built for banking duties in Yorkshire. When that line was electrified it was moved to similar duties on the Lickey, replacing the LMS's only ten-wheeler. That loco had been built by the Midland Railway in 1919. To get back to the GER, the previously-mentioned "Decapod" was the only other ten-coupled loco in the UK until the British Railways era 9Fs. As far as I am aware, the Decapod, built in 1902, was never used in passenger service. Although its axle loadings were well within limits, the all-up weight would have been too great for some bridges, but it proved its point, that steam could accelerate just as fast as the new electric railway that was being promoted in competition with the GER. With the electric rival seen off, the necessary bridge strengthening work was never done and the loco was redundant. It was converted to an 0-8-0 in 1906, and scrapped as non-standard in 1913)
Point of detail, you've overlooked the War Department 2-10-0s
Were some of the wartime 2-10-0s not assembled at what became Hainault depot? Or was that US Transportation corps locos? If so doubtless some were run over parts of the GE suburban, but there'd be no reason to send them to Chingford.