London to Birmingham - Route?

I have been asked to help find and risk assess a route from Birmingham to London (Southall) for the annual Sikh bike ride. Over 200 people do the ride. They have used A roads in the past which hasn't been the most pleasant of routes. Can anyone suggest an alternative route on B roads and quieter roads which

1. is direct and
   
2. easily navigable
   
3. not too hilly (as many riders will not be ideal bikes for a long run)
   
4. pleasant
   
   

The ride is late July and I plan to ride the route beforehand

Thanks