James wrote:
I read some previous threads on the speed cams at Tower Bridge, but
they didn't quite answer a query I have, I wondered if any of the
experts on these groups might no. I received a NIP (notice of
intended prosecution) not long ago for doing 32mph and it defines the
speed limit there as 20. I did to be fair see these signs, but always
understood that 30 was the legal minimum speed limit in the UK, and
that therefore signs indicating 20 were advisory. Is this still true?
Does anyone think I can challenge the NIP or the automatic penalty
offer of a delightful 3 points that will inevitably follow on this
type of ground? Anyone know of cases where people have challenged the
Tower Bridge cameras?

Not advisory, mandatory. It's only 30 unless otherwise notified. Pay up and
take advantage of the generous cash discount. Try and challenge it and
you'll lose. The restriction is there for a reason.