Tighter cabin bag rules will take effect on a major low-fare airline from Tuesday
Passengers travelling on easyJet flights will only be certain of being allowed to take hand luggage aboard if their bags are no bigger than 50 x 40 x 20cm.
This is slightly lower than the current size restriction of no bigger than 56 x 45 x 25cm.
This restriction remains but, should flights be particularly full, late-comers with luggage heavier than the new lower figure could face having to have their bags put in the hold.
EasyJet said: "If you bring one piece of cabin baggage no bigger than 50 x 40 x 20cm including handles and wheels, we guarantee it will always travel with you either in the overhead locker or, if necessary, under the seat in front of you.
"You can still choose to bring one slightly bigger bag up to the maximum size of 56 x 45 x 25cm including handles and wheels, but on some busy flights your bag may have to go into the hold."
The airline went on: "The bag guarantee is a way for passengers to gain peace of mind that their bag will travel with them onboard the flight. The guarantee is transparent and fair to all our customers and the result of in-depth customer research."
According to a Which? magazine survey, 40% of easyJet passengers will still fly with a maximum-weight bag and risk having their luggage put in the hold.
Meanwhile, from Monday, British Airways passengers will be able to use mobile phones as soon as their plane touches down at their arrival airport. Until now BA travellers were only allowed to use mobiles and other electronic devices once their aircraft had come to a complete stop and the doors were opened.
Rules preventing use of devices once a departing plane has left the gate remain.