New rules for carry-on luggage that have come in at some UK airports could confuse passengers, a lobby group says.
Some airports could not meet the government's standards
Twenty-two airports are relaxing the rules to coincide with extra security checks, but others, including the UK's second busiest, Gatwick, are not.
The Air Transport Users Council said it had voiced its concerns with ministers.
Airline Easyjet said there was "massive scope" for confusion and it was retaining the one-bag rule on all its flights regardless of the airport.
The Department for Transport said that travellers can now carry more than one bag on board, providing the airport has installed improved security scanners and depending on their airline's policy.
The restrictions, introduced in August 2006 in the wake of a terror alert, remain at Gatwick and other airports that do not currently meet government requirements for the one-bag rule to be relaxed.
Source: Department for Transport
Simon Evans, chief executive of the Air Transport Users Council, said: "We have told the government there is potential for confusion.
"Since August 2006, we have all been urging people to become acquainted with the one-bag rule and to read the [official] advice. Now the message has changed and there is no longer one consistent message."
Easyjet operates from 14 UK airports, seven of which have had the restrictions lifted, but has decided to keep the one-bag rule for all its UK departures. The airline charges passengers up to £8 to check in hold luggage.
Chief executive Andy Harrison said: "There is massive scope for customer confusion in an environment where UK airports are adopting different policies.
"The only way to maintain a simple and standard policy is to maintain our one-bag policy."
Easyjet's rival, Ryanair, maintains a similar rule on hand luggage although it charges up to £10 for each bag that needs to be carried in the hold.
Tom Kelly, spokesman for airports operator BAA, said the situation was "very simple".
He said: "What passengers should do is talk to their airlines. That was the position before the restrictions were introduced and that is now the position again.
"The good news is that passengers can have a choice. Because we've invested in staff, because we've invested in equipment, we can offer airlines - and those airlines that want to then offer it to their passengers - the choice of having more than one bag."
The Department of Transport asked airports if they could allow more baggage through but guarantee there would not be a drop in security standards and that queues would not become too long, putting pressure on staff to push baggage through faster.
Some airports, such as Gatwick, applied but were told their standards were not yet high enough to allow the one-bag rule to be relaxed.
Only passengers using South Terminal for connecting flights from Monday will be able to travel with more than one piece of hand baggage if their airline allows.
BAA, which runs Gatwick, says restrictions will remain in place at the North Terminal while engineering works continue to bring the airport up to standard.
However, from 11 February, passengers using the North Terminal on connecting flights will also be able to take more than one piece of cabin luggage.
Bristol, Luton, Leeds/Bradford and Liverpool John Lennon airports are among others yet to meet the standards.
Some airports, including Glasgow and Edinburgh, only received the go-ahead in the last few days.
Size limits on liquids and cabin baggage will still apply and airlines can place their own restrictions on the amount of hand baggage that can be taken in to their aircraft.
The government has stressed it is up to passengers to check hand-luggage policy with individual airlines.
British Airways will allow two pieces of hand luggage per passenger.
Virgin Atlantic says all passengers, regardless of class of travel, can carry two pieces of hand luggage into the cabin.
The dimensions of hand luggage must not exceed 56cm x 45cm x 25cm (22in x 17.7in x 9.8in approx), including wheels, handles and side pockets. This is equivalent to the size of a small roller suitcase.