IMO, I think there's a danger here of misunderstanding signs and their purpose.
The 'signs on approach' are the gateway signs in Mansell, set some way back from the junction- the point to which Hippocrates refers. We're not looking at signs situated at the junction which really rely upon other warning signs but the signs in Mansell. GSV shows where they are located, although not the signs themselves, and in the opinion of this adjudicator would afford any driver ample time to see and respond: they are not positioned such that a driver couldn't possibly avoid.
In my view a request for a review must fail because the adjudicator made a finding of fact which was one which they were entitled to make. OP, it wasn't that you turned into Mansell, it's that on doing so you did not act upon the very clear gateway signage far enough away to enable you to not contravene.
In my opinion.