A number of people, who remind me very much of alt.space people (it is left as an exercise to the reader to guess whether this is a nice thing to say about them), have plans for commuter airships.
See http://www.thinairgroup.com/TAG~airshipsportal.html "Our niche is crunching the numbers for these operations, and proving the viability of the concept for cutting-edge entrepreneurs."
Now, clearly, since the reason Mayor Ken is in favour of Cross (Cross? I was livid) rail is to whisk people from Heathrow to Canary Wharf in order to keep London at the centre of the 'moving money round the world and skimming the transaction cost off the top' business - cutting the journey time from 60 minutes to 46 - well worth the 16 billion quid I hear you cry - why bother digging an expensive hole when you can have a fleet of commuter airships? I suspect that there should be 3 routes - Heathrow <-> CW, Heathrow to CW via City West (Farringdon? Or maybe St Pancras to connect with EuroHole), Heathrow to CW via City East (Liverpool Street?).
Now all we need is to make up some numbers and find some venture capital.