"The Medway Handyman" gurgled happily,
sounding much like they were saying:

What I'd like to know is when the present 30 & 40 limits came into being
- and what braking systems were common at the time?

The default urban 30mph limit was introduced to the UK in 1935.

Hydraulic brakes were a real novelty at the time, and older stuff still
on the roads would still not have had front wheel brakes.