Decided to go up to Colinton today.
Met (pure chance/good timing) a CEC Countryside Ranger who was looking at the tree Smudge mentioned - because he had mentioned it here!
Seems the tree has been down for several weeks, it was cut through as a temporary measure by the Rangers and is awaiting for Forestry people to remove properly.
Apparently the only vehicle access is all the way from Colinton through the tunnel. There's still snow/ice down on some parts of the route.
Should be sorted soon.
Even better news - various sections of the route, and bits south of Colinton are due to be upgraded in the next couple of months.
A mix off drainage, mud scraping and whin dusting should make a big difference.
Any similar problems should be reported to countrysiderangers@edinburgh.gov.uk
NOTE Rangers don't cover North Edinburgh Paths Network.
Sites covered by CEC Rangers.
More info on Rangers.
UPDATE
Remembered that ranger said that it was better to get several reports about a problem - "don't assume that someone else has reported it".