Downloading .gpx files
You can download .gpx files from here. You can then upload them to your tom tom if you have one, and follow the routes while you drive. You may also be able to import .gpx files straight to google maps and follow from there.
On driving tests the examiner will only require you to follow a sat nav for twenty minutes out of thirty five, so these routes represent both the sat-nav part of the test, and also the examiner-led parts.
Note also that 20% of tests do not use sat navs at all, but require you to follow road signs.