Hi Geoff,

Curiously, all coal isn't the same ... LNER engines had wide fireboxes to suit Yorkshire coal, GWR engines had narrow, deep fireboxes to suit Welsh coal.

1924 British Empire Exhibition, both the LNER and the GWR claimed their loco (Flying Scotsman and Clun Castle iirc) was the most powerful. 1925 they swapped engines to test the claims, the locos that went to the other's system both hauled several wagons of the 'correct' coal.

Turned out the GWR Castles were the more powerful, led Gresley to make several changes to the LNER A1's.

Regards,