Britons visiting the US under its visa waiver programme will have to apply online at least three days before leaving in a move which could see people banned from travelling. The US Department of Homeland Security has announced that travellers must apply for permission online prior to travelling from January 12.2009 Passengers from the UK and other eligible countries will be able to make the application via the Electronic System for Travel Authorisation (ESTA) and stay for up to 90 days without a visa, if approved. But the US Department of Homeland Security plans -which replace the traditional handwritten forms - also stipulate that applications may not be submitted less than 72 hours before departure. And those who do not receive travel authorisation 'may be denied boarding, experience delays or be denied admission into the United States,' according to the US Embassy website. 'If you have to travel on short notice – say, the next day – you could still register online in the very likely hope that you would have success. 'About 99.5 per cent of applicants get approval within four seconds. 'If there should be a denial or if further processing of the registration application is necessary, then you've probably cut yourself too close to departure to apply for a visa at the Embassy.' 'That's why we strongly recommend that travellers register online with ESTA at least 72 hours before departure.