Hi. It absolutely is possible. I work fairly long hours in 'the City' and CC around Central London. I've never been on the Thames though, so can't say I do the ring. You don't actually have to. The rule of 'one calendar year' in actuality boils down to 'about two months'. Have a chat to the BW chaps at Paddington or give them a call if you want to confirm or deny this.
For the last few years I've happily lived in and around London, and when I say 'around', yes my commute is sometimes almost two hours. I have moored as far out of London as Milton Keynes - working my way back down via the mainline trains to Uxbridge - and to Bishops Stortford - also served very well by trains. Yes, sometimes my commute is almost two hours each way but sometimes I can walk to work. Sometimes I have to slog about 20 minutes to the towpath from the train station but sometimes I'm moored practically on top of the station.
Camden, Paddington and Islington are now listed as 7 day moorings and all Central London moorings have Wardens. I've always stayed 14 days at Islington with no hassle and have never stayed at Camden because it's always full.
The bottom line is that just about anything is possible if you are up to the graft and if I'd have read these forums before taking my challenging lifestyle on, I'd have thought it impossible. I'm very grateful that I began living the life before reading about it here...
Take the 'the canals are getting full' protests with a grain of salt as for ever new CC in and around London, there is someone moving to dry land/out of the area or taking up a permanent mooring. Also, if the worst case scenario does happen and the mooring you come to is full... and this is stupendously rare as most moorings in London allow double breasting and accommodate quite a few boats... then simply move on to the next one.
I'll probably regret posting this as the 'you arent' doing it properly' hellfire posters come out of the woodwork but I just want to redress the balance with actual facts from someone who does indeed CC in London.
Hope this helps xxx