I think one could argue the sign is inadequate, being placed badly placed, well after one would be preparing to turn right, and also set at the back of the footway on a lamppost. The text would be almost impossible to read before turning, for instance. However, they will just send you a Fob-Off letter if you submit representations, so you'd hae to take them to London Tribunals with the full PCN penalty in play.
Why not submit representations on something like these lines: -
Dear Sirs
Re postal PCN <number> dated <dd/mm/yyyy> for Reed Road, (entrance to LIDL).
I deny responsibility for the above PCN on the grounds that the contravention did not occurr, due to badly placed signage. On receipt of the PCN, I visited the location on foot to see what sign I had contravened.
On the day in question, approaching the turn into LIDL, I did not notice the sign which is placed very badly after the actual turn, and much to the left of the carriageway, being mounted high up on a lamppost at the back of the left-side footpath. It also contains text with the times of the restriction. This text is impossible to read on approach, until a committment to the turn has been made. It seems to me that if the council are going to impose draconian penalties on people making this turn within the restricted hours, that more attentions should have been made and more money spent on ensuring clear visibility of the sign, and its positioning for motorists approaching the turn.
I therefore request that the PCN be cancelled and the council cease enforcement until better placement of the sign is made.
Yours faithfully
Indeed, looking at the whole set-up, the yellow box junction could be considered unlawful, because it is not at a junction of two roads, but at a gated entrance to commercial properties. In addition, one must question also whether a "No Right Turn" sign can be applied in the same circumstances. By applying this No Right Turn, the council are adversely interfering in the commercial interests of the business located there.
Hopefully, others will comment on this, as I am not an expert on this sort of thing.