Cut across north London area entering course almost on time (8)
I believe the answer is:
transect
'cut across' is the definition.
(I've seen this before)
'north london area entering course almost on time' is the wordplay.
'north' becomes 'n' ('N' can be a synonym of 'north').
'london area' becomes 'se' (abbreviation for South East).
'entering' indicates putting letters inside.
'course almost on time' becomes 'tract' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'n'+'se'='nse'
'nse' placed inside 'tract' is 'TRANSECT'.
Can you help me to learn more?
(Another definition for transect that I've seen is " Cut across".)