I can't speak for London, but I can speak for riding fixed or single on flat or hilly/mountainous route. I love it. I currently have 3 bikes: a fixed gear Bike Friday Pocket Rocket, a single speed Surly 1X1, & a geared Surly Cross Check. I'm leaving the Cross Check geared but I have been tempted to switch it to single as well. My Pocket Rocket has a flip flop rear wheel fixed on both sides. It is my main commuter as well as my main training ride for fast aggressive groups. Fixed/single in bad weather works really great. That is one reason my 1X1 mountain bike is a single speed. If single speed 100 mile mountain biker racers can complete a mountainous (12,000 -14,000 feet of climbing) course almost as fast as the open racers, then commuting on one can be no problem.