It's just paint on the road. There's a lot of meaningless paint on roads these days. Like the dashed line and crossed out section on that left turn. It's meaningless and you can drive right over it. Someone decided it would make the junction safer forcing a driver into a position where they can see better. Normally they would move the kerb and extend the pavement but paint is cheaper.
I've no idea what the current situation is, but there used to be (in the old days) two types of "ghost islands", ones with dashed outlines, which could be driven over with a reasonable excuse*, and ones with solid outlines, which needed a bloody good excuse for you to encroach onto them, but nobody seems to bother much about them now, at all - and I'm not even sure the solid-bordered ones still exist.
* I would, for instance, drift right onto the last bit of the central dashed area before a right-turn box, as at the Dog & Doublet junction, to avoid unnecessarily slowly down a car behind who is going straight on southwards there.
As for meaningless paint - I once spent a long time trying to find an official interpretation of the red band up the middle of Fairway, before giving up. I decided that it's just meant to frighten you a bit, in general.
If people have nothing better to do, they could look at the Prince of Wales car park exit onto the genuine One Way St Thomas Street and see the direction sign opposite - and compare that with the exit of the Metropolitan Bar's car park onto Tixall Road, with its lack of a sign.