Paul Weaver wrote:
I think tomorrow night I'll continue round and drive through some
residential streets in W14 if the mayor and his cronies insist on
closing major thoroughfares.

I don't know the answer to your question of why Warwick Gardens is
barriered off at night (apart from it being a prestigious street full
of very wealthy residents), but I wouldn't rush to judgement that it's
because of a Mayoral decision. I have a feeling that this arrangement
has been in place for a good few years, predating the creation of the
Mayor and TfL.