Does anyone know if it's possible to hire, for a day or three, a good-quality carbon/ti road bike, in south London or Surrey?
Head for the hills dorking?!
I've not used them but British Bike Hire might have what you want. http://www.britishbikehire.co.uk/RoadBikeHire
Further afield for carbon-fibre is Totally Bikes (Newbury, Berkshire): http://www.totally-bikes.com.
They do collection and delivery to the London area. Bikes can be picked up at a triathlon shop in the Windsor area if necessary. Deposit required, but you can even borrow an ex-Ben Swift Pinarello if you want to be really flash.
I recommended you for On Your Bike which is biggest retailer of road bike and London Bikes.
I know Pilgrim Bikes at Westhumble Station (bottom of Box) have road bikes to hire, but IIRC they're more basic than you're after. May be worth a call though.
Bit late now, but I've recently used Livelo Performance Bike Hire in London. They delivered the bike to my airbnb and then collected it again when we were leaving.
Good service and good quality bikes. We used a Cannondale Supersix, not sure if they have others available, but worth a look www.livelo.co.uk.