Most of London is supposed to be "smoke free" under the Clean Air acts of the 50's and 60's, when London pea-souper smogs were common, fewer houses had central heating and many relied on open fires as their main source of heat. See http://www.uksmokecontrolareas.co.uk for details. You are allowed to use "smokeless" fuels.

On the other hand, I don't think anyone has seriously enforced this in decades, as most people now have central heating, smog is mostly a thing of the past and the motor car comes in for most of the pollution stick. On the other hand, given the global warming arguments these days, we may see this change .....