Actress Anna Friel has said she was still "completely in shock" at the unexpected decision last week of British oil and gas company Soco to pull out of exploration plans in Africa's oldest national park, something she has been campaigning for on behalf of the wildlife charity WWF.

But while delighted at the decision, she warned vigilance was needed over what happened next in the park, situated in the volatile east of the Democratic Republic of the Congo. She vowed to step up her own efforts as a conservation campaigner, saying: "It's still not safe and we really can't rest on our laurels."

In the weekend that actress Angelina Jolie was given an honorary damehood, Friel defended celebrities using their fame to promote causes they care about.

"Well-known people are given a profile in the media and it seems to me to make sense to use that profile responsibly to highlight the causes closest to their hearts. In my case it concerned the unnecessary exploitation of Virunga and helped, for the time being at least, to preserve a precious world heritage region.

"I was delighted my daughter was able to join me as I feel it's equally important for us to educate and hopefully pass on our sense of responsibility and concern for issues that are not just in our own backyard. It is surely important to stand up and be counted, if you believe strongly enough in the stance that you have taken."

In what is one of the greatest successes by wildlife conservationists in many years, several groups had been campaigning against the Soco presence, especially after the DRC government indicated it was likely to give the company permission to drill. Last-minute mediation between WWF and Soco led to a joint statement being issued, just as Friel was planning a Trafalgar Square demonstration against any drilling in the area, home to the last remaining mountain gorillas in the world.

It marked the end of what had become a personal issue between the Yorkshire actress and the oil company, which had attacked her for making a film about the Virunga from over the border in Rwanda. "It was ridiculous," said the stage and film actress. "I went out there to make a film with Stephen Poliakoff about the park and the threat posed to it but because of violence in the Congo we couldn't cross the border so we filmed in Rwanda with the park behind me. And I quite clearly say that in the film. To start attacking me was an attempt to get away from the point."

Friel, who went to Virunga initially to see the gorillas, along with her then eight-year-old daughter Gracie, ended up becoming the public face of the WWF campaign after hearing about the danger posed to the area. "I suppose it was quite a political thing to do but once I had seen the gorillas, and got into things a little deeper, and realised just how serious the situation facing them was, then it was the only thing to do.

"It's a region of outstanding beauty. Mainly because it is untouched. Lush virgin rainforests stretching further than the eye can see. It created for me a deep feeling of calm, peace and tranquillity. I felt honoured to share it's serenity.

"My involvement in what was a wider campaign was minor, compared to the people who are devoting their lives to this cause, but I'm proud to have been part of it."

Virunga was designated a world heritage site in 1979 but since then has become one of the world's most volatile regions. The park has been at the heart of intense fighting between armies and militias like the Mai Mai rebel group for more than 20 years and is home to tens of thousands of people who fled the genocide in Rwanda. Many park rangers have been killed, by poachers or militias, and last month the Virunga chief warden, Emmanuel de Mérode, was shot and seriously wounded.

The joint statement with WWF and Soco read: "Soco has agreed with WWF to commit not to undertake or commission any exploratory or other drilling within Virunga national park unless Unesco and the DRC government agree that such activities are not incompatible with its world heritage status.

"We will complete our existing operational programme including completing the seismic survey on Lake Edward which is due to conclude shortly. The company confirms its previous statements that no Block V drilling commitments have ever been made. The conclusion of this phase of work will give the DRC government vital information it will need in deciding how to proceed in Virunga national park."

The threat to the last remaining natural habitat for mountain gorillas has been further highlighted in the documentary by director Orlando Von Einsiedel, Virunga: The Movie, which is being screened in the US to critical acclaim.

WWF experts believe that, if managed sustainably, Virunga could be the source of 45,000 jobs through eco-tourism, hydropower renewable energy and fishing. Thousands already rely on the park and its bordering lake for food and water and past examples of oil exploration in Africa by multinational companies have left whole swaths of land polluted.

"The trip was, to coin a cliche, life changing and life affirming for me. My upbringing made me aware of the fragile nature of our planet, and the need to protect it. We are not all imperialist interlopers in this global community. There are so many inspiring people out there fighting the fight, daily, to protect our planet. Robert Ddamulira from WWF told me how the age of easily obtainable oil is over, and the few reserves left are in unique places like Virunga."