The government has told Brother Paul McAuley, who runs an civil association in the jungle town of Iquitos and promotes indigenous rights, to leave Peru within seven days and never return.
The interior ministry revoked his residency permit on the grounds he has participated in political activities "such as protest marches and other acts against the Peruvian state which constitute a breach of public order".
The expulsion would mark an abrupt end to the campaigning of a Briton revered by indigenous groups and reviled by the authorities and sections of Peru's media, which in addition to "Tarzan" has branded him a "white terrorist" and "incendiary gringo priest".
McAuley said he would fight the expulsion. "I am heading to my office now to see if it's possible to appeal. I'm not sure what's going to happen," he told the Guardian today. "I received the order yesterday so I've got six days left."
One tribe offered to hide him in its forest village and a Peruvian woman offered to marry him so he could get a visa. "The support has been extraordinary but I'm going to fight this legally. I'm not going to stay if I'm not allowed," said McAuley.
The 62-year-old, a lay member of the Catholic De La Salle teaching order, is a high-profile opponent of government efforts to parcel up three-quarters of Peru's rainforest for oil, gas and ethanol.
Peru is home to 70m hectares of Amazon, second only to Brazil. Deals worth billions of dollars have brought in helicopters, barges and pipelines and raised expectations of being a net oil exporter.
"Peru's government are clearly determined to brook no opposition to their plans to carve up the Amazon. The government has already initiated a campaign of persecution against indigenous leaders. Now it appears to be going after their allies," said David Hill of the advocacy group Survival International.The interior ministry did not immediately respond to request for comment.
The Portsmouth-born McAuley has travelled the Amazon helping indigenous activists to protest the incursions and set up a civil association, Red Ambiental Loretana, in the humid rivertown of Iquitos in Loreto, a northern region bordering Ecuador. He travels on a scooter and by boat.
The missionary was awarded an MBE for setting up a school in Peru's capital, Lima. Had he not already given it away some years ago he said he would have sent it back to the Queen to protest British companies' involvement in the Amazon. He has embraced elements of Amazonian spiritual belief based on the concept of energy.
Clashes between police and activists in Bagua last year, which McAuley was not involved in, cost dozens of lives and rocked President Alan Garcia's government.
Environmental and indigenous groups expressed outrage at the expulsion order and some promised vigorous protests. "The reaction has been tremendous, everybody across the region is full of indignation," said McAuley.
Julia Urrunaga, a policy adviser to the Environmental Investigation Agency, said an indigenous champion was being persecuted for challening big corporations. "I feel totally ashamed as a Peruvian and extremely sad to lose someone who has so positively affected the lives of people here."
The advocacy group Amazon Watch said McAuley had been under investigation for years but had refused to be intimidated. "The probable impact of the expulsion - certainly intended by the Peruvian state - is to create a chilling effect on international support of ongoing local indigenous struggles for their rights."