The day the sky turned black...

It is often assumed that modern living has intensified pollution levels in the capital but in fact it has improved since the 1950s when factories belched out smoke on a daily basis. In 1952, London was enveloped in a toxic blackout for four days.

The fumes claimed 4,000 lives and many more died later from bronchitis and pneumonia brought on by the poisoned air. Even cows at Smithfield Market suffocated. When the thick smog blocked all visibility, London came to a standstill and business faltered. This disaster inspired the 1956 Clean Air Act, which did much to eradicate pollution in Britain's towns.