Free Traffic Legal Advice

Well, here is the location and the sign, which is certainly not "stuck to a tree and not particularly visible.". I don't think an adjudicator would agree with you on its visibility, although you could claim "sign clutter" or maybe the restriction would have been noticed if a sign had been place either side of the restriction.
https://maps.app.goo.gl/rnEGWbeLB5UJDKNG6
However, before the total ban was put in place there was a timed "Flying Motorbike" sign on the centre island which was illuminated. The current sign is not lit so counts in your favour particularly as the central width sign is lit

The other things counting against you is there are several advance signs here: -
https://maps.app.goo.gl/rBGdysLQEvsmSD5MA
and another one here, although this seems to have got twisted round so it is not so visible on approach to Federal Road: -
https://maps.app.goo.gl/2FvLdAepmqRR7F4G6
but there's yet another sign: -
https://maps.app.goo.gl/ozQBj9uq6P5VXN9UA

So in all, there are three advance warning signs. Clearly the restriction to all except permit holders is designed to prevent all manner of commercial traffic from accessing the business area via the residential area. The original timed restriction obviously was set-up to prevent wide and large vehicles from access, but they have now changed it to all vehicles.

Frankly, I cannot see any credible appeal to take to London Tribunals, but others may see one. I haven't yet trawled through the PCN to see if there are any fatal errors.

HOwever, just have a look at this incredible sign madness on GSV of 2020 !
https://maps.app.goo.gl/3ZY2osNYxAcaBejg9
And councils wonder why they are so unloved !!