Police arrested 11 people staging a climate protest outside Biggin Hill airport in Kent on Thursday as part of the wider against the expansion of Heathrow airport.

Several had chained themselves to the perimeter fence.

A similar protest was held outside Farnborough airport in Hampshire.

Both airports reported business as usual.

The protests came in the middle of a week-long climate camp outside Heathrow, the world's busiest international airport, whose organisers have promised unspecified "direct action" against expansion plans.

Scientists say air transport contributes heavily to global warming, noting that the carbon dioxide and water vapour emitted at altitude are four times more potent than at sea level.

The government is committed to tackling climate change by cutting CO2 emissions but also backs a rapid expansion of air travel, which is set to double in the next 25 years.

The arrests on Thursday bring to 16 the total number of arrests connected with the climate camp since Sunday.

The protest comes at the height of the holiday season, three months after a blazing jeep was used to attack Glasgow airport and a year after police thwarted what they said was a plan to bomb airliners flying out of Heathrow to the United States.

Organisers declined to say what the "direct action" would entail, but did say they would target British Airways and airport operator BAA.

The climate camp is just to the north of Heathrow, directly in the path of a proposed third runway and close to BAA's headquarters.

Organisers expect around 1,500 people to join the camp, even though torrential rain is forecast this week.