By 1850, due to the expansion of railways, NE England began to lose its status as the key supplier of coal to London & SE England. Rail-borne Midlands & Yorkshire coal vied by cost & speed, while collier sailing brigs made coal transport relatively expensive & slow.
As mentioned previously on this blog, Palmers at Jarrow re-established NE predominance by building iron screw colliers, which lowered costs, increased speed, and reduced dependence on weather. (It took a few more years for the advent of the TIC to improve navigability & port facilities on the River Tyne, but that's another story.)
I had thought that Palmers built the first iron steam screw collier in 1852, but I am proven wrong by at least two previous ships .....