London Loops: COVID-friendly short mixed-terrain routes

I am looking for routes that fill the following criteria:

• Circular, start/finish somewhere in London's famous London
  
• Between 30km and 70km
  
• Mixed surface; think cycle paths, very quiet roads, the odd very mild bit of off-road
  
• Ideally suited for riding on a hybrid bicycle
  
• Not for racing along, more to cycle slowly and savour
  
  

As so many of us only get one chance per day to exercise at the moment these would be great to find more of.