Dr Ken Lamden from the HPA said the low uptake of the MMR jab in the late 1990s was partly to blame.

BBC: Measles outbreak confirmed in Lancashire by HPA

The biggest idea is to extend London's Low Emissions Zone, a scheme pioneered by Ken Livingstone, Mr Johnson's predecessor as mayor.

ECONOMIST: Cleaning up London��s dirty air

Shadow business secretary Ken Clarke said public sector pay had to reflect "the current low level of inflation".

BBC: Spending chief urges pay freeze

In Japan, according to Ken Okamura, a strategist with Dresdner Kleinwort Benson, the birth rate has been so low that the working-age population will actually start to decline next year.

ECONOMIST: What happens to pay if prices are static, or falling?