Your Garmin help, please

So I've been using MapMyRide for routes and it works fine out in the countryside. Having used it for creating routes through London recently, I find that there is often a pink line which the 800 directs me down instead of following the purple line I plotted. Pretty. Fucking. Annoying.

I just tried using Bike Route Toaster and it freezes with a "Retrieving Route Information" message and a spinning circle thing in the top left corner. Also. Pretty. Fucking. Annoying.

Also just tried Garmin Basecamp, but only seem to have access to the crap maps that come installed with the 800.

Can anyone suggest where I am buggering this up?

To access detailed maps for basecamp go here http://garmin.openstreetmap.nl/

Choose generic routable, choose uk from the europe drop down box.
You will then get links to the windows exe file to install the maps on a pc, a link for the img file if you wish to place it on your garmin and also a link to a zip file for the map installer on a mac