The five reported users of the LONDON mark are:
Middlesbrough Pottery, 1834–52
Isaac and Thomas Bell, Albion Pottery, 1860–63
Carr & Sons, Low Lights Pottery N. Shields, 1844–c 1900
Malkin, Walker and Hulse, British Anchor Pottery, Longton, 1858–64
Fell & Co, St Peters Pottery, Newcastle on Tyne, 1817–1890
I'm hugely grateful to Gary Spence for getting in touch recently regarding a pair of children's plates, one of which has the impressed London anchor mark (see below).
R C Bell (Tyneside Pottery, 1971) shows a Burn & Co printed mark, very similar to that used by Thomas Fell. It has two sea horses around a shield underneath which is written 'B.&Co.' He suggests that the mark was intended to deceive, as Burn tried to 'pass his wares off as those of the leading Tyneside firm of the day'. I don't have a photo of the Burn printed mark, but here is the Fell mark below.
For interest, below are a selection of London marks that appear North Eastern pottery. The last image is a scan from R C Bell's book, and appears on a plate with an 'Albion' printed mark with the signature 'I&T.BELL.'. R C Bell suggests that different numbers on this kind of mark signified different potteries.