Waterway distances are shown, not footpath distances.
When using imperial units, it is normal to use statute miles (1609 m) upstream of Teddington and sea miles (1853.3 m/6080 ft) downstream from Teddington.
The text
"London A1, Manchester (A6)"
means
"London via the A1,
Manchester via the A1 and
then the A6
Kilometer distances and
carriageway information
are taken from driver location signs