#Oxon elections: curious #GreenBelt campaign promise issue

A letter sent to all #Oxon DC candidates invited them to sign a pledge “to vote against any building on green belt”.*
Three replies (below) wrote that
a candidate cannot sign a planning policy pledge on pain of being barred from all committee meetings on any related application !
CityVoice Question: Surely this negates the purpose of manifestos, local democracy, etc ??
[CityVoice Comment:] >
“The statement that a candidate cannot sign a planning policy pledge appears to stifle candidates’ right to debate / freedom of speech PRIOR to the election, no?
Could it be that this prohibition applies only to councillors stating a pre-formed opinion after their election ?
What if one writes a planning policy in a manifesto??
It’s like excluding all pro- or anti- Europe MPs from a Parliamentary vote on Europe !
Looking closer, the statements argue that a committee member cannot have a pre-formed opinion on the application – not the principle.
Is a councillor to be excluded from planning committee decisions just because of having signed off on a policy ?
What nutty aspect of the planning law is this? How can we do politics and planning at all on this basis ?
We know committee decisions are required to be “quasi-judicial”, but surely a candidate can have a declared policy for voters to choose ?
Cityvoice.co exists to encourage local involvement with planning knowledge and ideas – this claim appears to prohibit candidates from campaigning for their beliefs! How can local democracy survive like this ?”
( Debate from lawyers [constitutionalists?] would be welcome. )
Info: two of the 3 thoughtful letters:

The third – similar, and equally polite and thoughtful – reply is from Jackie Walker, LAB, Henley – which we have currently mislaid !