Basecamp insists on taking a long diversion

As I don't have access to that map it's difficult to be sure. You say you're not avoiding any type of road but does that include any seasonal road closures as I've seen similar when those were selected. Another thing to try is a different routing profile from the one you've selected. If neither work then it's likely a map error so you'd need to report it to the map maker.

Thanks for your suggestion Sussamb. I turned off everything, told it to take the shortest route and changed the profile from car to motorbike, however it had no effect.

If anyone has any other ideas I'd be grateful.

Dave

Sometimes there are errors in the routing data for a map.

It is possible to use different Profiles for different segments of a Route in BaseCamp.  Be warned that your device may not allow this and will recalculate the route to what is shown.

In this case, I would try adding points on the intended route north of elbow, the elbow and south of the elbow.  Open the route properties, right click on the north point, choose edit via point and change the Profile at the bottom to Direct.  Repeat with the elbow point.

This isn't something I've had to do, so you may have to play aroung a bit - adding points at the north/south diversions and/or choosing points before/after the points mentioned.  Someone else with experience can provide better details.

If a device doesn't allow profile changes in a single route, then multiple routes will be required.  Your case might get by with two routes..  One ending before the elbow and one starting after the elbow.  I would leave a gap in the two routes.

Other cases will require three or more routes using a combination of routing (e.g. Car, Hiking etc.) and Direct profiles,  

I've encounter that problem here in the US.  Basecamp refuses to route across a bridge over the Snake River from Oregon to Idaho and I could never find a way to force it cross.  And it was a well establish paved road.

I finally ended up by breaking the route into two parts.

The same problem occurred when routing from Arizona into Mexico at the Los Algodones border.  It is a quirk of BaseCamp that seems to occasionally pop up.

I can confirm this in the U.S. also.  There is no identifiable reason for Basecamp not to route along a road but for whatever reason it will route through a neighborhood then back to the road a half fine down-route.  I found that adding two waypoints along this stretch of road resulted in the route traversing it.  Using "Direct" would have been an option as well.

Invariably a map error in that there is a break in the data at a point. I've found that a couple of times when looking at the HERE map data on their website. Also what sometimes catches people out is seasonal road closures. In both cases it's not a BaseCamp fault but the map etc