Airlines are ignoring their own carry-on baggage limits.

Despite a huge security crackdown on flights to and from the UK, US and some parts of Europe, passengers are being allowed on board with over-sized and overweight hand luggage.

Some of the biggest culprits are the airlines' best customers - the frequent flyers. And on transcontinental flights the problem is exacerbated by self-service check-in.

Airline crews and their luggage are included in X-ray searches. Depending on the point of embarkation, passengers are being asked to remove watches, belts, keys and coats as they pass through security, some must remove shoes, and in many countries passengers are warned that bottled water and drinks are banned, that strict limits apply to medicine, and that cosmetics and personal items such as toothpaste need to be presented for inspection in a zip-locked plastic bag.

But the policing rarely extends to the size of carry-on luggage, although airlines clearly advertise maximum size and weight at check-in, on web sites and company literature. The traditional space under the seat in front has been reduced to make room for electronic controls for in-flight video entertainment systems, placing extra demands on overhead lockers.

Qantas did not respond to a request to discuss its hand baggage policy despite clear breaches of its well-publicised size and weight restrictions and warnings of charges for items in excess of its limits. It says on its website that for bulky carry-on items you may also need to purchase an extra seat.

Earlier this year, British Airways introduced steep charges for checking in more than one piece of luggage for long-haul flights - a change it claims will affect only 2 per cent of its customers. It nominates maximum size for carry-on bags but advises: "You must be able to lift your bag unaided into the aircraft overhead locker". Any wonder that passengers try to crib on the amount stuffed into hand luggage and briefcases.

Heavy luggage is clearly a risk for passengers and crew if it is dislodged during turbulence.

President of the Flight Attendants Association of Australia Steven Reed says crew have suffered a significant number of injuries from handling passengers' over-the-limit bags.