At least eight Britons dead in Tunisia terror attack

So far, Tunisian authorities have confirmed the nationalities of 10 of the dead, with a Belgian and a German identified alongside the British victims.

Prime Minister David Cameron has warned that the public should be "prepared for the fact that many of those killed were British".

Scotland Yard today said police travelled to Tunisia to help investigate the killings and officers are also interviewing tourists returning at British airports.

Holiday firm Tui, which runs the Thomson and First Choice brands, said that a number of those who died were its customers.

Gunman Seifeddine Rezgui, a 23-year-old Tunisian aviation, was said to have laughed and joked as he targeted British and French tourists and sprayed them with gunfire. He was shot dead by police.

Extra consular staff along with police and experts from the Red Cross will arrive in the North African country today to help the victims and their families.

Cameron, who today chaired a second meeting of the Government's emergency Cobra committee, said his "thoughts and prayers are with the loved ones of those killed or injured".

Speaking in Downing Street, he said: "These savage terrorist attacks in Tunisia, Kuwait and France are a brutal and tragic reminder of the threat faced around the world from these evil terrorists."

He added: "We are working with the Tunisian authorities to identify the final number of British casualties but I'm afraid that the British public need to be prepared for the fact that many of those killed were British."

Cameron insisted "we will defeat" Islamic extremists waging terror around the world.

Speaking outside the Tui UK building near Gatwick Airport, Peter Long, joint CEO of Tui Group, said he was "deeply, deeply shocked".

"And our whole organisation is reeling with pain to see the suffering that has taken place in Tunisia."

He added that the company's directors from locations across the UK confirmed that so far it has repatriated 1,000 customers and that 5,400 still remained in the area, with everything being done to help those who wanted to return to get on flights.

However, the company was unable to confirm how many of its customers had been killed or injured in the tragedy.

Travel agents' association Abta said an estimated 20,000 people were currently on holiday with its members in Tunisia but there were also others who had travelled independently.

Islamic State has claimed it is behind the attacks and has reportedly identified the gunman by his jihadi pseudonym Abu Yahya al-Qayrawani,

The worst such attack in Tunisia's history came on the same day a man was found decapitated after an attack by suspected Islamic extremists on a French factory and a Shiite mosque in Kuwait was bombed, killing at least 25 people.

Although the attacks do not appear to be directly linked, they come as Islamic State marks one year since it declared a caliphate. Islamic State leaders also called for their followers "to make Ramadan a month of calamities for the non-believers".

"Once again, cowardly and traitorous hands have struck Tunisia, targeting its security and that of its children and visitors," Tunisian president Beji Caid Essebsi said.

Harriet Harman, acting Labour leader, said the party's "deepest sympathy and thoughts" go out to the families and friends of the victims.

She said: "These shocking events, as well as the attacks in France and Kuwait, remind us of the constant threat the world faces from terrorism, and the need for constant vigilance.

"It is disappointing that the impact of these crimes will also be felt by Tunisia's economy, not least its growing and important tourism industry.

"We will back the Government as it works to help the families affected and counter these extremist ideologies which have so brutally taken the lives of the innocent."