Although this re-routing has good results - providing an early service and retention of route knowledge - its origins were somewhat different.
In the early days of Sectorisation infrastructure costs were allocated on a prime user/avoidable basis.
The sector that later became Regional Railways was Prime User for some sections of the route via Grantham. Their early morning and late evening services required longer Signal Box opening hours (in effect, an extra shift), and because they were the Prime User they received all the (not inconsiderable) extra costs for this. In simple terms by not using the route at these times the signalling costs were alloocated to the next user down the hierarchy, Freight, and Regional Railways escaped them. On the route they transferred to they only paid avoidable (=marginal) costs, because they weren't the Prime User, and the signal boxes were open and paid for by the Prime User.
Regional Railways at that time had something of a reputation for escaping costs by exploiting the system to 'dump' them on other Sectors rather than actual cost reduction management.
