Welcome Pippi. You make a good point but actually the proposed forum is trying to define a neighbourhood. If this is a worthwhile thing to do, it really needs to be villagey.

To compare: we live in HOP, SE23 (which is mostly Lewisham borough), Devonshire Road, in Forest Hill ward and would be constitutionally barred from contributing to the proposed forum.

Any sensible definition of the HOP community would surely also include the Rec, One Tree Hill and St Augustines and these all lie in the borough of Southwark (SE23 postcode if I am not mistaken!).

It is tempting to blame estate agents (c.f. perceived expansion of East Dulwich and Brockley) but in this case these are mostly administrative borders and odd in my view that anyone would want to define a neighbourhood this way.