Nearly there!
Tried a new (very flat) route and nearly made the magic 5 k in 30 minutes target I have set myself. Must admit a very fit young lady sprinted past me on 1 Km before the end and that geed me up considerably.
So I have found the answers, I need to go round the route beforehand with a JCB to flatten it completely and persuade a team of pace setters to keep me on track.