Helicopter pilots in central London are instructed to follow the Thames, to avoid flying over built-up areas as far as possible.

CNN: London helicopter crash prompts safety questions

The survey had been "extremely well supported... even in the most built-up areas where you might not expect people to watch birds, " Mr Bashford added.

BBC: NEWS | UK | Fewer birds spotted in UK gardens

The problem with installing micro turbines in built-up areas is two-fold.

CNN: Can 'small wind' reap big rewards?

All but 3, 000 of Jerusalem's 200, 000 settlers live in outlying neighbourhoods that ring the city and avoid the built-up areas where the city's 270, 000 Palestinians still live.

ECONOMIST: Jerusalem

The bad news is that we have yet to succeed in preventing large numbers of fatalities in built-up areas away from the tornado culture when an F5 shows up.

FORBES: The Great Tornadoes Of 2011 Put In Perspective

It's not clear if the idea is for an upgrade or a new line, which would somehow have to find a route through built-up areas in the two cities.

BBC: Making tracks and political points

"We have an average of 33 reports of tornadoes in the UK each year but these are especially rare in built-up areas and there has not been one of this strength in many years, " said a Met Office spokesperson.

BBC: NEWS | UK | England | West Midlands | Tornado hits Birmingham

The addition to the coalition's armoury this week of American A-10 Thunderbolts and AC-130 gunships, lumbering aircraft equipped with fearsome cannon that can hit targets in built-up areas with less risk than fast jets of killing civilians, could tilt the balance in Misrata and elsewhere.

ECONOMIST: The battle for Libya

People living in built-up or former industrial areas, such as south Wales, the West Midlands and London, also tended to be less happy, while rural areas, such as Rutland, Orkney and Shetland, were among the happiest.

BBC: Welsh people top 'most dissatisfied of UK'