Energy company Cuadrilla has began exploratory drilling in the English countryside despite on-going anti-fracking protests at the site.
The project has been subject to repeated delays because of high-profile demonstrations entering their ninth day, designed to halt delivery of trucks and equipment to the plant.
A Cuadrilla spokesman confirmed that drilling had begun at 11.15am on a 3,000ft vertical well. "We will be there for two to three months,” they added.
Sussex Police said two people - a 19-year-old woman and a man - were arrested at the site today, both on suspicion of assaulting police.
Campaigners fear the project at Lower Stumble, near Balcombe, West Sussex, could lead Cuadrilla to go on to conduct hydraulic fracturing, or fracking.
The controversial method of fracking involves high pressure liquid being pumped deep underground to split shale rock and release gas supplies.
Opponents of fracking fear water contamination and environmental damage could happen as a result of fracking, as well as small-scale earthquakes.
Vanessa Vine, of Frack Free Sussex, said she was "absolutely livid and incredulous" at the start of the drilling. "This is a violation of our geology that could threaten our water, fresh air and our children", she said.
"There is a political mania around this. I have no faith in our governmental process, and I feel like Balcombe is sacrificial.
"This is going to spark the biggest environmental movement we have seen."
Since protests began more than 30 people have been arrested, mainly on suspicion of obstructing deliveries. Among those detained were Natalie Hynde, 30, the daughter of the Kinks' Ray Davies and the Pretenders' Chrissie Hynde, along with her boyfriend Simon Medhurst, 55 after the pair reportedly superglued their hands together around a gate for two hours.
Police have had to implement a daily security operation around the test site's entrance as dozens of anti-fracking protesters have turned out to halt deliveries.
This week Cuadrilla's chief executive, Francis Egan, reacted to concerns surrounding the drilling by saying his firm has “no intention of ruining the countryside and won't ruin the countryside” and insisted the practice of fracking was safe.
Whilst he acknowledged his firm's activities had been delayed as a result of protests in West Sussex, he said “significant” amounts of oil and gas could be made available through fracking in the UK.
However, Mr Egan said that today's drilling was for oil exploration and that the company would not be fracturing the well as part of this process.
Brenda Pollack, Friends of Earth’s South East Regional Campaigner warned that if the Government continued to back fracking as a means of extraction, communities will find themselves in the firing line.
“People are right to be concerned about fracking. It threatens their environment and quality of life and will mean more climate-changing emissions are pumped into the atmosphere. And there’s plenty of evidence that it won’t lead to cheaper fuel bills," she said.
“It’s time to end the nation’s damaging fossil fuel addiction and build a clean energy system that doesn’t cost the earth.”
Former Government Energy Adviser Lord Howell highlighted the sensitive nature of the issue earlier in the week after suggesting fracking could be used in “desolate” north east England without any impact on the surrounding environment.
He went on to provoke further criticism when he attempted to clarify his comments by suggesting he was actually referring to “unloved” areas of the country such as Lancashire.
His attempt at clearing up the controversy prompted Deputy Prime Minister Nick Clegg to urge Lord Howell to be quiet. Mr Clegg also suggested on his regular LBC radio phone-in that the Conservatives were getting “over-excited” about the controversial extraction technique's potential benefits.
Additional reporting by PA