A Christian village in Lebanon has been saved from being overrun by Islamic State forces by a British-built watchtower.

According to the Daily Telegraph, the Tango 10 watchtower – one of a chain of 12 built at high speed along the Lebanese border with Syria during the last few months – was all that stood between Islamic State and the village of Ras Baalbek.

The tower, which is platform for artillery, covers the pass leading to the village. A member of the British team responsible for the construction of the tower, made of shipping containers welded together and wire cages, told the newspaper that it had foiled an attempted invasion. "When the invasion came, a line of vehicles split off and headed for Ras Baalbek," the team member said. "Then they stopped and looked up at the watchtower and all its artillery waiting for them. They turned around."

Of the Islamic State fighters, one of the team, made up of former officers and engineers, said: "They are drugged to the eyeballs and think they are going to paradise. It's a pretty tough enemy for anyone."

The watchtowers stretch half-way along the country's eastern border and more are planned. They create 'overlapping arcs' of sight, meaning that the border is far better protected. "You can't imagine what it was like when we got out here first," one former officer said. "There were a few guys behind some tyres filled with rocks with a 50 cal [machine gun]."

"You have to start security somewhere," said another. "We are not building the Maginot line. People are scared. They've all seen the decapitations on YouTube. They know what Isil want to do."

While Islamic State is unlikely to be able to mount a successful invasion of Lebanon, it is finding increasing support among Sunni Muslims there, who make up around 25 per cent of the population and feel marginalised by the existing power structures. Many are unimpressed by the support given by the powerful Hezbollah organisation to Syria's President Bashar al-Assad, and Islamic State is known to be recruiting among disaffected young men.

The country is also coping with vast numbers of refugees from Syria. More than 1 million have crossed the border since the fighting in Syria began.