Barking and Dagenham have long had 'form' on off-carriageway parking. Just have a tootle around their residential streets and you'll see lots of off-carriageway parking and not a sign in sight. It seems they tolerate, (i.e do not serve PCNs), in lots of areas. Yet we still see PCNs like yours every so often. It's difficult to give advice if there are no signs allowing it, as the contravention is clear.