Security restrictions on hand luggage are being relaxed at 22 UK airports from today onwards.
But some airports, including the second-busiest Gatwick - are not affected by the government directive as their security systems have been deemed insufficient.
In addition, many airlines are keeping the restrictions in place as part of their own policy.
The Department for Transport is urging travellers to make sure they know what limits are in place for their flights.
"Before departing we strongly suggest you check with your airline on the cabin baggage arrangements for your particular journey," a statement said.
Airport authority BAA said it was advertising the change of regulations at its six airports where the restrictions were being relaxed.
"To help passengers further, we will also be asking airlines to ensure that passengers clearly understand airline baggage policies at the check-in points before they pass through security," a spokesperson added.
Limits on the size and number of hand luggage items have been in place since the foiling of an alleged plot to blow up transatlantic flights in August 2006.
Commenting on the changes, the British Air Transport Association (BATA) said it was a "welcome start".
"What happened in August 2006 meant it was very difficult for airports to cope with security and this was an attempt to take some of the burden, sort of relieve them of some of the workload," claimed BATA secretary general Roger Wiltshire on Radio Five Live's Wake up to Money programme.
"What we see now is proof that the airports can cope with the new security regime and it means that queues are shorter than we have experienced in the last 15 months.
"There's a lot more to be done I think to reduce some of the hassle from the security process, but this is a good start."
Airports where one-bag restriction will no longer apply:
Aberdeen Benbecula Birmingham Cambridge Cardiff Edinburgh Glasgow Heathrow Inverness Islay Kirkwall London City Manchester Newcastle Plymouth Prestwick Southampton Southend Stansted Stornoway Sumburgh Wick