Speed limits exist to promote safe usage of our roads. The legislation prescribes different classes of speed limit for different classes of roads, It also allows some leeway to local authorities, in their capacity as road authorities, to determine the appropriate speed limit for particular roads or stretches of road.
Where the law does allow options to local authorities to determine appropriate speed limits, it is entirely a matter for local authorities to make those decisions, having regard to all the relevant factors. Central Government has no role in this process, and it would not be appropriate for me to comment on the best speed limit for a particular road.
I would add that, in making decisions on speed limits, the most important consideration for local authorities must always be road safety.