I've used a white, Fiat 500 Twin Air as my daily driver in London for nigh on two years. My accountant recommended that I get it through my company as the BIK was so advantageous. It's a terrific little car. Perfect for city driving. The Twin Air is road tax exempt and is also exempt from the Congestion Charge until 2016. It can fit in the smallest of gaps and parking spaces and I can leave it anywhere in the city, safe in the knowledge that it is nigh on invisible to 'undesirables'.
Even with the turbo disengaged, its 800 CC engine is easily capable of keeping up with traffic. It will happily blat along on a motorway at 80+ for hour on end. The steering is ultra light, the car turns on a sixpence and the cabin is a really nice place to be. It has air con, bluetooth, iphone connectivity. I'm six foot tall and an adult can sit directly behind me in some comfort - try that in a new mini. A full tank of petrol costs less than £35.
I love it to bits.