Nothing. Nothing is really any good and the best available, such as a conversion of the Citroen C1, is outrageously expensive. As much as a Prius. Mitsubishi recently announced a price of £33,000 for its tiny i-MIVC electric car, and that was after a government grant of £5,000.
With nuclear power closing down, not much hydro electricity and alternative energy creation comprising only a small percentage in the UK, any electric car is likely to run on coal fired power so is only 'clean' in its immediate environment. Also the UK is running out of the means of developing enough power for its needs anyway because there has been insufficient investment in power generation. The only sensible argument for electric is that they are good for short runs from cold, and start-stop use, which is where internal combustion engines are at their least efficient. That's why milk floats were electric. The best compromise is a Prius or a Honda Insight hybrid.