I'm sure it used to be listed as 158 1/2 in some old timetables, and I always assumed (or maybe read) that was via the Erewash - but I was never sure if it meant Erewash - Nottingham - Manton or Erewash - Trent - Leicester.
This is presumably via Leicester and Derby?
164.75 miles would've been the shortest route between St. Pancras and Sheffield via Derby in the 1970 BR Passenger Timetable, as all the St. Pancras to Sheffield services ran either via Derby, or reversing at Nottingham. The distance via Nottingham (reverse) was a fraction over 166 miles. In the late 1960s, before the Melton Junction to Nottingham (via Widmerpool) route closed the distance from St. Pancras to Sheffield via Corby and Nottingham was just a fraction shorter than via Derby at about 163 miles.
In May 1973 a number of St. Pancras to Sheffield services reverted to using the direct route from Trent Junction via Toton (158.5 miles). This coincided with the opening of Alfreton & Mansfield Parkway station, giving a slightly quicker time to/from there by avoiding the reversal at Nottingham.
DOWN SERVICES
1E78 1025 St. Pancras to Sheffield
1E72 1620 St. Pancras to Sheffield
1E65 1805 St. Pancras to Sheffield
UP SERVICES
1M04 0715 Sheffield to St. Pancras
1M11 0745 Sheffield to St. Pancras
1M13 0830 Sheffield to St. Pancras
1M79 1500 Sheffield to St. Pancras.
1M88 1645 Sheffield to St. Pancras.
I was lucky enough to have a cab ride in June 1973 (a Saturday) on 1E78 going down, and 1M79 coming back. (I have the detailed log of the running somewhere in my files). The return run was made more interesting in that because of Engineering Works at Market Harborough, which started at midday we stopped at Loughborough instead of Leicester, then took the North to East chord at Syston to travel via Melton Mowbray and Corby, making the distance 169.5 miles.