According to GSV there's an advisory sign only yards before Khartoum, between Opex Fashions and Khartoum.
Personally, I would focus on the non-prescribed white on blue sign shown in GSV and the video: School streets - Restricted Access Term time only.
No such permitted sign.
1. It is restricted to term-time only: then the council need to obtain the SoS's authorisation to a non-prescribed sign. But they haven't, because the only prescribed sign is every week, term time or not.
2. The restriction isn't term time only, which is what's conveyed by the advance sign. In which case IMO the signage fails the LATOR test because in combination those in the know might be tempted to drive into the area outside 'term time' but still be breaching the traffic order's prohibition.
In either case, IMO you have strong grounds for appeal.