The cabin baggage ban on laptops and tablets on direct flights to the UK from six countries will be in place by Saturday, the government has confirmed.
Passengers travelling from Turkey, Lebanon, Egypt, Jordan, Tunisia and Saudi Arabia must put big electronic devices in the hold.
BA, Easyjet, Jet2.com, Monarch, Thomson and Thomas Cook flights are affected.
Transport Secretary Chris Grayling said the move was in response to an "evolving threat" from terrorism.
He told the Commons the government's decision was thought necessary to protect the safety of UK passengers, but would not give any more detail.
"We have taken the steps for good reasons," said Mr Grayling.
The ban applies to any device larger than 16cm long, 9.3cm wide or 1.5cm deep. It includes smart phones, but most fall inside these limits.
Under the new rules, all large electronic devices, including Kindles and similar e-readers, must be packed into luggage going into the hold.
Mr Grayling told MPs he would write to insurers to ask them to be mindful of the changes.
The new security measures would be brought in "over the coming days and no later than Saturday 25 March", said a Department for Transport spokeswoman.
She added that passengers "should go to the airport with the expectation that the measures are already in effect".
So far, only Easyjet has confirmed to the BBC that the restrictions are already in place.
UK carriers affected by the ban include:
- Easyjet - It introduced the ban on Wednesday. The airline said passengers would face extra security checks and advised them to arrive early at their airport. It says it is contacting affected passengers ahead of their flights to let them know the new rules. Up to three Easyjet flights a day are expected to be hit by the new security measures.
- British Airways - It issued a notice to passengers on Tuesday, saying passengers would face additional searches and questions, and were likely to be called to their boarding gates earlier. Travellers part-way through their journey or about to start a journey in one of the affected countries who felt unable to immediately comply with the new rules can rebook their flight.
- Jet2.com - It says Jet2.com and Jet2holidays customers travelling from Turkey would face extra security checks and the new hand luggage restrictions. Its service from Turkey to the UK starts on Monday, by which time the measures would be in place, a spokesman said.
- Monarch - It says it will increase the paid-for hold luggage allowance by 3kgs free of charge to allow for the extra weight of electrical items. The airline runs a summer service from Turkey from 29 April, so no flights will be affected until then. It says it will remind its customers of the new travel rules by email.
- Thomas Cook - It says customers flying to the UK from Turkey and Egypt should pack devices into their hold luggage to be checked in before going through security. The company advises holidaymakers with questions to call them on 01733 224 536, or, if already on holiday, to check holiday documents for in-resort contact numbers.
- Thomson - The first affected flight for Thomson and First Choice customers departs early next week. The carrier said it was "currently working through operational plans and the best way" to notify affected customers.
Overseas airlines affected are Turkish Airlines, Pegasus Airways, Atlas-Global Airlines, Middle East Airlines, EgyptAir, Royal Jordanian, Tunis Air and Saudia.
The ban follows a similar move in the US, where officials say bombs could be hidden in a series of devices.
Mark Shepherd, from the Association of British Insurers, advised travellers to check their insurance policy covers valuables placed in the hold.
He said some might find they have additional cover under a household contents policy for gadgets outside the home.
"Wherever possible, travellers should keep valuables, including tablets and laptops, with them on flights and, if travelling from destinations affected by the new regulations, it may be sensible to leave valuables at home," he added.
"If devices are damaged during a flight, there's also the potential to seek compensation through the airline."