A British oil worker held by Islamic militants for more than 18 months has been freed in a military operation.

The United Arab Emirates has reported its military freed Douglas Robert Semple, 64, who was kidnapped by Al Qaeda in the Arabian Peninsula in Yemen while working as a petroleum engineer.

Foreign Secretary Philip Hammond confirmed the release of a British hostage by UAE forces in a military intelligence operation.

Mr Hammond, who is in Iran, said: "I'm pleased to confirm that a British hostage held in Yemen has been extracted by UAE forces in a military intelligence operation.

"The British national is safe and well and is receiving support from British Government officials. We are very grateful for the assistance of the UAE."

A statement carried by the UAE's official WAM news agency said Mr Semple was taken to the Yemeni port city of Aden before being flown by UAE military aircraft to Abu Dhabi.

He was greeted at the airport by the British ambassador and taken for medical checks at a hospital.

A picture of Qassim al-Raimi, leader of Al Qaeda in the Arabian Peninsula, from a Yemeni wanted poser (Getty)

The statement did not reveal where in Yemen Mr Semple had been held or provide any details on the rescue operation.

The UAE is part of the Saudi-led and US-backed coalition that has been launching airstrikes against Shiite rebels in Yemen since March.

The UAE's official statement said Semple had been working as a petroleum engineer in the Yemeni province of Hadramawt when he was kidnapped in February 2014.

It said Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed Al Nahyan telephoned British Prime Minister David Cameron last night to inform him of the operation.

Al-Qaida has been making inroads amid the chaos of Yemen's civil war.

Yemeni security officials told the Associated Press on Saturday that al-Qaida militants seized control of key areas in and around Aden, once one of the world’s busiest ports, and are expanding there in the wake of fighting between the Shiite rebels known as Houthis and an array of anti-rebel forces backed by Saudi Arabia.

Backed by heavy airstrikes, anti-rebel forces pushed the Houthis out of Aden last month.

Houthi rebels, Al Qaeda and a Saudi-led coalition of Arad forces are locked in a power struggle in Yemen (Getty)

The Houthis, who deny Saudi claims they are supported by Iran, overran the capital of Sanaa last year and eventually forced the Yemeni president into exile in Saudi Arabia.

Washington considers al-Qaida's Yemen branch to be the most dangerous offshoot of the global terror network and has repeatedly targeted it with drone strikes.

Several Britons have been recently kidnapped in war-torn Yemen, where abductions are frequent as armed tribesmen and al Qaida-linked militants take hostages in an effort to swap them for prisoners or cash.

British-born American Luke Somers, 33, was shot dead by his Al Qaida in the Arabian Peninsula captors in December as they fought US special forces attempting to extract him and South African teacher Pierre Korkie.

He was kidnapped in September 2013 in the capital Sanaa while working as a photojournalist.

In July 2014, Mike Harvey was released five months after being captured in Sanaa.

His abduction was the third to take place in Yemen in only two weeks. On February 2 last year, another Briton working with an oil services company was kidnapped in Sanaa. Two days earlier, a German citizen was also kidnapped.