You know the feeling: you buy a budget airline ticket and turn up at the departure gate only to discover that you have the wrong sort of hand baggage. It might be too big for the “sizer” at the entrance to the plane. Or you may have one too many items – such as a handbag as well as a laptop case. The error could cost you £50.

Cabin baggage limits on flights are maddeningly complicated. Airlines decide their own rules on the exact dimensions and weights of hand luggage.

Many “legacy” carriers such as British Airways and North American airlines have a generous two-item allowance for cabin baggage.

But budget airlines in Europe are much more restrictive. Most charge for anything bigger than a small backpack, laptop case or handbag. They deploy different dimensions for the free cabin baggage item, and for a paid-for trolley bag.

European consumer groups say every passenger should be allowed to carry a rollalong case, as well as a “personal item” such as a handbag or laptop bag, free of charge. Sixteen national bodies from across the EU, under the European Consumer Organisation (BEUC) umbrella, say They want a consistent and generous allowance for what you can take into the aircraft.