Vaughan Hardy says….
A correspondent in the Times suggests that the South of England starts near to our town as, for example, from Grimsby to Grantham the pronunciation of the word “bus” is clearly the northern variation with a hard “U”.
In Stamford and Bourne the word is pronounced as elsewhere in southern England, “burse”.
What clearer definition of north and south could there be?
The Midlands therefore does not exist and puts Grantham firmly in the north.