Fifty-one of these were built at the GER's Stratford Works and the remaining 20 by William Beardmore and Company.

[6] After the grouping the LNER ordered a further batch of 10 locomotives from Beyer Peacock of Manchester, and these were delivered with running numbers 8571 to 8580 to Gorton shed.

A further ten were ordered in 1928 to ease a power shortage caused by the stalled development on a new class of 4-6-0 locomotives, and the cancellation of the planned suburban 2-6-4T tank locomotive due to the adverse press publicity caused by the Sevenoaks derailment of 1927.

The first substantive change was the fitting of Lenz poppet valves to the 1928 batch (from new), and six of the ex-GE locomotives (8516/19/25/32/33/40).

As newer power became available, the locomotives’ low axleload made them ideal candidates for transfers elsewhere.

In the 1946 scheme, the class was allocated the 1500–1580 block(their 1924 numbers with 7000 removed from them), with gaps for the two withdrawn locomotives.

B12s were selected because they had the Westinghouse brake, and were generally acceptable because their low-axle loading gave them a very high route-availability.

They operated widely over the network and were fitted with a "vacuum/air proportioning valve" to allow the driver of a local pilot engine (used where double heading was necessary because of gradients) to control the brake throughout the train.

In 2016, Hornby launched a brand new tooling of the B12 in a super detail form with LNER apple green and BR lined black with early and late crest liveries.