Spoke to the BW staff at Limehouse Basin on Saturday.
It is possible to do the Thames Ring in a RIB. In fact they were very keen to get me on the canal!!
If I go from Brentford on the Thames, round the Grand Union Canal, up to the Regents Canal, through Camden and back down to Limehouse I am told it will take 2 days!!
Sounds like a plan but I'd need somewhere safe to keep the boat for the overnight and somewhere to sleep. (Sleeping on the boat is not that appealing!!)
All I need I'm told is
1) BW Windlass £7
2) BW Key to access toilets, showers and some lock gates.
3) Visitor Licence £50 (I think)
You don't need a boat safety certificate as I'd be on the canal system for less than 30 days.
I will keep you all posted if this goes ahead over summer but we have to "finish" the Thames first (Henley to Cricklade!)