DAVID Cameron will today update MPs on the Tunisian terror death toll in a House of Commons statement, with Whitehall sources indicating it could "reach into the high twenties", making it by far the worst such atrocity since the 7/7 attacks in London 10 years ago.

As hundreds of holidaymakers made their way back to the UK, the Foreign Office updated its travel advice to warn that further terrorist attacks in Tunisia were possible and urged any Britons remaining in the country to be vigilant.

Ministers in London and Edinburgh held emergency meetings to consider the practicalities of helping families involved in the tragedy, travel advice and security for holidaymakers. Downing Street lowered its flags in respect for the dead.

Several relatives expressed concern about the lack of information from both the UK Government and tour operators.

Holly Graham, from Perth, whose parents Billy and Lisa are missing, said: "Thomson are like they're just reading off a piece of paper. The Foreign Office; they just tell you they've got no information."

But Theresa May, the Home Secretary, who chaired a meeting of the UK Government's Cobra contingencies committee in Whitehall, rejected claims that the Foreign Office had reacted too slowly to the terrorist attack, saying it was imperative the UK Government "got it absolutely right for families" and that that sometimes took time.

She explained how British officials had been struggling to identify some of the victims because those gunned down in the "appalling" beach massacre would not have had passports or other forms of identification with them and some victims were being moved between hospitals in the country.

"What's important is that the information is absolutely 100 per cent correct when it is given to a family," declared Mrs May.

"If you can imagine...because of the circumstances of the attack, people won't have had documents with them; they won't necessarily have had phones.

"Some people are being moved between hospitals, so the team on the ground are making every effort to ensure that they get accurate information."

Asked if the beach had been targeted because of the high number of British tourists using it, she replied: "This is still an ongoing investigation and we are working very closely with the Tunisian authorities in relation to this.

"I've seen no evidence so far that this was targeted because there are British tourists there, but, of course we must recognise this is the most significant loss of life in a terrorist attacks since 7/7."

In Edinburgh, Nicola Sturgeon chaired another meeting of the Scottish Government's Resilience Committee to ensure her administration was doing all it could to help the victims of "this senseless attack" and their families.

"I would like to offer my heartfelt sympathies to everyone who may have lost a loved one in this attack," she said.

She noted how the threat level for the UK remained at severe and that counter-terrorism measures were in place to respond to this. The advice from Police Scotland, she said, was to "stay vigilant and alert".

Meantime, Mrs May, asked about reports four major terror plots had been foiled in the last few months, confirmed a "number of plots" had been stopped recently.

"Over the last 10 years it's estimated that something like 40 plots have been disrupted here in the UK," she said.

"The threat has become more diverse over time. It has changed over time. That's why it's important for us to sustain the counter-terrorism capabilities of the agencies."

The Home Secretary said the UK Government would be introducing a counter-extremism strategy to tackle radicalisation.

"We want to work with families and communities so if they are seeing signs of somebody being radicalised, if they are concerned about the behaviour perhaps of their son or daughter or perhaps of somebody's friend that they are actually able to come forward to the authorities and talk to us about this so we can perhaps stop somebody from going down that path of radicalisation," she added.