On August 19, British police armed with billy clubs clashed with groups of climate change demonstrators near the headquarters of Heathrow airport's operator.

The skirmishes took place in a field near the airport operator BAA's building after mostly peaceful marches from a camp where campaigners, who seek to draw attention to the impact of aviation on global warming, have been accumulating all week.

About 50 marchers flanked police and got to the BAA car park by slipping through residential gardens but they were herded into a designated area. Police chased another group into fields, hitting some with truncheons, before surrounding them.

Police said no one had yet been detained on August 19, although 45 campaigners have been arrested over the course of the week. BAA said the airport was operating normally and there was no disruption to passengers.

The protesters want Heathrow's expansion plans dropped and the growth of air travel halted. The protest comes at the height of the holiday season at the world's busiest international airport that handles nearly 70 million passengers a year.

"There's been so much media hysteria about baby-eating anarchists. What we're saying is that this is a peaceful protest. The only thing we are armed with is the consensus of the scientific community," said activist Peter McDonell.

Scientists say air transport contributes to global warming, and the carbon dioxide gas and water vapor emitted by aircraft are four times more potent at high altitude than at sea level.

The British government says it is committed to tackling climate change and plans to set legally binding targets for cutting CO2 emissions -- but it also backs an expansion of air travel, which is set to double in the next 25 years.