In reply to Rog Wilko:
I use Brouter to generate long distance routes. Its advantage over Google Maps is that you can select different route profiles. So a fast road bike might give a different route to a touring bike (quiet paved roads) which would be different again to a mountain bike route.
I have the Locus Maps app on my phone, linked to Brouter. The combination is generally excellent except that (a) Locus Maps loses GPS too easily and (b) LM over estimates height gain and loss. I usually factor them by 0.7 and that then gives very similar results to Google Maps. Note that tunnels also cause issues for Locus Maps. Tunnels are not flagged in the Brouter gpx file, so LM assumes that the track follows the Earth's surface. This is more of an issue in the Alps than the UK.