It would reduce the number of speeding and parking offences because people should know what the restrictions are and would behave accordingly. It would reduce the amount of money spent on "policing" violations. It should also reduce the number of road signs which have proliferated and are a blot on the landscape.
Once upon a time we had this. You could tell by the road you were on what the speed limit was. You knew when you could park and when not. Road signs were UK wide and useful.
Then the management of these was delegated to the Local Council and now we have chaos. A proliferation of speed limits which are set to different criteria in each district. A rash of new speed limit signs has appeared across the country. It's often genuinely difficult to know what the speed limit is.
And parking is a nightmare – each council has its own laws and signage. It's quite possible to get a parking ticket when trying really hard to be parked legally. On Cricklewood Broadway in north London, three boroughs meet. Each has its own parking rules and they vary wildly.
I would like to see the criteria for speed limits, parking restrictions and road signage standardised across the UK, even if they continue to be administered locally.