Travellers on all flights to and from the UK are being advised to ensure mobile and electronic devices and laptop computers are powered up following the latest security advisory from the Department for Transport.
The DfT is advising passengers that "some routes" to and from the UK, in addition to all flights to and from the US, now require devices carried in their hand luggage to be switched on at security.
It did not specify which routes these are, effectively meaning that any flight to or from the UK carries this requirement.
In a statement, the DfT said: "For obvious reason we will not be commenting in detail on the routes affected. We will work with the aviation industry to minimise disruption as far as possible."
Any passenger who is not able to show the device or computer operating may be denied boarding.
New regulations affecting US flights have been in place since July 2 (see news, July 3) and are thought to have caused little disruption at airports. However, the start of the holiday season may prompt problems as peak passenger levels are reached at major airports, particularly as the rules will include items such as electric razors and cameras.
A DfT spokeswoman added: "If it is an electronic device, it should have a charge."
Heathrow airport declined to say what would happen to any device that was not charged or to the passenger carrying it.
A spokeswoman said the airport "cannot comment on security measures" and added: "It's a very delicate situation, we are not going to comment on what happens here or there."
The airport has posted staff in terminals advising passengers where charging points are and giving advice on where they can be bought.
The spokeswoman added: "The bottom line is come to the airport with devices charged – and that applies to anything electronic."