At 10pm on Sunday night, the RIB (rigid inflatable boat) carrying environmental activist Emily Hall pulled up alongside a coal freighter travelling at 15 knots down the Thames Estuary.

Hall was scared. She'd had weeks of sleepless nights leading up to this protest - her first water-based "action".

She was also dreading a possible hostile reaction from the crew of the ship the Greenpeace protest group was about to board.

A mate used an extendable pole to hook a caving ladder on the side of the moving ship and another activist started climbing. But three of the ship's crew began unhooking the ladder. They had to plead with them to stop for their own safety.

Hall heard this in the darkness. "By the time I got to the top of the ladder, I was totally preparing myself for this angry crew but there was no one around."

In the darkness she found her cohorts and they began hanging banners calling for an end to coal-fired power stations and climate change.

Next they abseiled down the side of the ship. The idea was to put themselves between it and the dock, preventing it from delivering its load of "dirty" coal to the Kingsnorth Power Station. But the captain ignored them, along with two Greenpeace swimmers in the water and the RIBs in his path.

After docking, he put the hose on the protesters dangling off his ship. Hall was soaked. By 2am she had been hanging for three hours and the first signs of hypothermia set in. She was shivering uncontrollably and getting sleepy. Her brain was starting to shut down.

A colleague noticed and had her abseil down to a rescue boat and she was whisked to safety while 10 other activists stayed and were arrested by Kent Police.

To some, this sort of stunt may sound dangerous, reckless or even objectionable - but to 35-year-old Hall - Greenpeace UK's activist and logistics support person - it's part and parcel of her dream job.

"I don't usually get scared but I do get overawed that my life has become so exciting," she says. "I've got the job I've always wanted."

It's been 13 years since the former beauty therapist from Havelock North hung up her electrolysis kit and left on her big OE. After a stint nannying in Sydney, she headed to Munich to meet a mate at the infamous Beerfest.

Afterwards they bussed back to London where Hall planned to stay for a few weeks, but she never left.

She spent several years leading a "hedonistic carefree lifestyle" and travelling the world before deciding that what she really wanted to do was save it.

She came home for a year to study environmental science in Nelson and got stuck into the environmental movement volunteering for the Green Party, the Nelson Environmental Centre and the local GE Free pressure group. Hall then returned to London, and starting as a volunteer, worked her way into a job with Greenpeace UK two years ago.

Her paid job within the "actions unit" requires her to help organise the legal support, equipment and logistics and coordinate activist training.

But being involved in actions is not part of her job description. She volunteers to be at the activist coalface - literally.

Much of Hall's recent protests focus on climate change and trying to bring an end to coal-fired power stations and poisonous carbon emissions.

She's been locked inside a smokestack, up to her ankles in coal dust, abseiled down a 200m smokestack face and scaled the sides of the coal freighter.

Last week she was arrested in Italy during a Greenpeace operation targeting the G8 Summit, a protest she jokingly refers to as "The Italian Job".

On day one of the summit, 100 activists from around the world broke into four Italian power stations to stage actions demanding G8 heads of state take action on climate change.

On day two, Hall and a team from the UK broke into a 1980MW power station Civitavecchia, just outside Rome, and painted "G8 STOP THIS" on a giant dome. She had been concerned the activists may be treated badly by Italian police but instead "it was the most relaxed arrest I've ever encountered".

The protesters were arrested on three offences, two of which were criminal damage but Hall can't understand what the third offence is "because it's written in Italian". Hall is unsure whether the Italian police will actually charge the protesters. With many Greenpeace actions involving "criminal" activity, charges are never laid, or are dropped.

However, Hall's greatest claim to fame stems from the one time the police did press charges against her.

Her name and face were splashed on the front pages of British newspapers last year as one of the "Kingsnorth 6", a group of activists that broke into the Kingsnorth power station in Kent to protest plans to build a replacement coal-fired station.

Hall and five men climbed up the inside of a 200m-high smokestack, then Emily - a novice abseiler - was one of two daredevils who went over the edge to spray-paint UK Prime Minister Gordon Brown's name down the side of the chimney.

A photo of her apprehensive face as she perched on the edge of the tower was, according to a colleague, the image which lead to closing down the station.

"I wasn't scared. It was higher than anything I had climbed before but I'm not afraid of heights and I knew I was in safe hands with the others in the team," she says.

"But after hanging off the side for three hours using rollers and holding heavy gear I was in a lot of pain. My hands were raw and it took all my strength to climb back up to the top again."

The six activists were arrested and charged with causing an estimated £30,000 ($76,000) worth of criminal damage, and the court case made history.

They admitted trying to shut the station down, but argued they were legally justified on the grounds they were trying to stop greater damage caused by fossil-fuelled climate change.

Greenpeace witnesses included Nasa climate change expert James Hansen and a representative of the Inuit community of Greenland who described watching villages "eroding into the sea".

After a week-long trial, the jury was persuaded and acquitted all six. Hall wept in the dock.

"There had just been so much stress in the build-up to the verdict, and we knew if it went in our favour it was going to make ripples," she says.

It was the first case where preventing property damage caused by climate change has been used as part of a "lawful excuse" defence in court.

The New York Times listed the "Kingsnorth defence" in its annual list of the most influential ideas that will change our lives. The story of the "Kingsnorth 6" has been made into a documentary A Time Comes by UK film-maker Nick Broomfield.

However Hall has also copped the criticism, as she discovered when reading comments about the documentary on YouTube.

"It's frustrating when people give you shit about that because it's their planet too," she says.

Often flak comes from townsfolk who are worried their livelihood is being threatened when Greenpeace targets local power stations. But other critics claim Greenpeace's activism is too radical, too alarmist and has led to a decline in membership and support for the organisation.

Hall is adamant that the direct actions are effective and vital.

"I do understand how what we are doing may seem extreme but we have no time left."