The bodies of energy worker Mark De Salis, understood to have been from Sheffield, and a female friend from New Zealand were discovered with gunshot wounds near the coastal area of Mellitah in the west of the country, according to a Libyan security source.
The woman, who has not been named, was described as a “close friend” by Mr De Salis’ family.
Mr De Salis, who had been working in working in Tripoli in Libya for six years, was remembered as a “decent and incredibly loyal man and he was loved by many”.
In a statement, released through the Foreign Office, his family said: “The family of Mark De Salis are shocked and devastated to hear about Mark’s death in Libya.
“Mark had been working in Tripoli in Libya for six years.
“He worked for First Engineering and was currently working as a power manager bringing generators to Tripoli to provide electricity.
“Mark enjoyed his work in Tripoli and liked the Libyan people.
“Mark enjoyed travelling and had travelled extensively.
“He was a decent and incredibly loyal man and he was loved by many.
“He will be sadly missed by his family and friends.
“Mark was with a close friend from New Zealand who was also killed and our thoughts are with her family at this sad time.
“We would ask that our privacy is respected at this time.”
Meanwhile, a gruesome photograph which is claimed to be of the dead pair has been posted on Facebook.
The picture, which was taken at night, shows two people lying face down on sand.
Local authorities said last night that they have not ruled out robbery as the motive for the attack.
However photographs showed what appears to be a picnic blanket with their belongings spread out on it, alongside a backpack.
Both bodies have been taken to Tripoli for post-mortem examinations to be carried out.
Mellitah is near the town of Zuwarah and 60 miles west of Tripoli.
The area is home to a large oil and gas complex co-owned by Italian company ENI.
Foreign Office officials have already urged the Libyan government to hold a “thorough investigation” into the murders, noting that its Charge d’Affaires has raised the shooting with the Libyan authorities.
The Foreign Office said it was liaising closely with the government, adding: “We call upon the Libyan government to carry out a thorough investigation into this tragic incident and to continue to do all it can to bring to justice the perpetrators of this appalling crime, as it strives to build strong rule of law in Libya.”
The killings come a month after a US teacher was shot dead in the eastern city of Benghazi, after which the Foreign Office said further attacks against Westerners were likely.
The area the murder victims chose to visit had been tense since the recent arrest of four armed US servicemen at a nearby checkpoint. The four, who were attached to the US embassy, were later released amid speculation that they were preparing evacuation plans for US diplomats.
Security experts say Islamist violence directed at expat workers is an increasing concern across north Africa. The Foreign Office advises against all travel to most parts of Libya, including Benghazi, and against all but essential travel to coastal areas to the west and east, including Tripoli.
Last month Libya was named as one of the countries posing an “extreme risk” to human rights by UK-based risk analysis company Maplecroft.