This is Money reports that the prospect of Britain becoming "too dangerous to visit" could wipe out £400 million in takings from overseas tourists.

It predicts a £30 million bill for hospitality and refunds over the next few days and a £10 million loss to productivity.

However, experts also point to the example of last year's London bombings, and indeed the 9/11 attacks which did not stop people flying.

Meanwhile, Sky News reports that the travel industry is shrugging off the possibility that the terror alert will have long-term implications.

Sean Tipton, from the Association of British Travel Agents (ABTA), said:

"We expect very little effect from this. It will take a lot more than a terror threat to put off the average traveller."