Traffic calming is a “substitution” of the hazard. It, like unexpected construction, forces drivers to slow down due to the road not being psychologically safe to drive fast on.
Speed limits are an “administrative control” on the other hand.
People will drive as fast as they (possibly incorrectly) feel is safe, and a lot goes into that, of which speeding fines are only one very small part. If you really want safe streets for pedestrians and motorists, it is just not as effective an option.
Additionally, I’m level certain that Tory austerity is not really a viable excuse here, because I’m sure that there are ongoing efforts to “alleviate the traffic problem” by adding capacity. It’s not that the money doesn’t exist, it’s that the money doesn’t exist for this. Because elected officials aren’t interested in this, because they’re more interested in fine revenue and keeping car people happy.