Armed men abducted the couple on October 4 at the beach resort they run
Armed men abducted the couple on October 4 at the beach resort they run Western Mindanao Command / STRINGER

A British man and his wife rescued this week from Islamist captors in the Philippines' south say they were chained and threatened with beheading if they didn't deliver a ransom.

The couple, shaken but unharmed, told their nearly two-month ordeal to reporters after escaping during a firefight Monday between Philippine troops and the Islamic State-linked Abu Sayyaf group.

The husband, named by British authorities as Alan Hyrons, painted a "very humiliating and degrading" life in captivity, with little to eat in a haze of constant fear.

"They chained our legs... It was very difficult, but we endured because we believe in God," his wife Wilma Hyrons said.

"One of them treated us well, but then he told me he would be the one assigned to cut off my head if the money does not arrive on time," she added.

Armed men abducted the couple on October 4 at the beach resort they run on the southern island of Mindanao, which makes up the southern third of the Philippines.

They were taken to Jolo island, which is the stronghold of the kidnap-for-ransom gang Abu Sayyaf, which has carried out some of the Philippines' worst attacks.

"We tried to scream but no one comes because they have the guns," the wife, who has Philippine origins, said.

She said the men pointed guns at her face, ordering her to call her brother so he would sell all their assets to raise their ransom, which the couple did not state.

Their chance for escape came after several days of firefights between the military and the kidnappers, which saw at least five of the gunmen killed.

"It's something you see on films and you take it to be a film. But in real life it's terrifying," the husband said, describing the final gun battle.

"There were only 10 of them when we escaped... It was the commander who got hit first so I told Alan, let us run. We should not wait here to be killed," the wife added.

Muslim separatists have led a decades-long insurgency in the south of the Catholic-majority Philippines, which has led to the death of tens of thousands of people.

While the government has negotiated peace with the largest group, the Moro Islamic Liberation Front, hardline factions allied with the Islamic State group are not part of the accord.

Abu Sayyaf has previously kidnapped foreign missionaries, businessmen, Western tourists and merchant seamen.

Dutch birdwatcher Ewold Horn, who was kidnapped in 2012 in the southern Philippines, was killed in May during a firefight between his Abu Sayyaf captors and the military.