As a budget airline, Ryanairis famous for its low fares, but another thing it has become notorious for are its strict rules on luggage. While the airlineclearly sets out its rules when you book, as well as on its website, people continue to be caught out by them.

A recent change to Ryanair's baggage policy saw it increase the size allowed for the free underseat bag that comes with even the most basic fares. In the past, bags had to be 40 x 25 x 20 cm, but as of last year, passengers can bring a bag of up to 40 x 30 x 20 cm. This small item can be a laptop bag, handbag, rucksack, or any item that fits within the dimensions to fit under the seat in front of you.

For an additional fee, which varies depending on route and availability, passengers can bring a second cabin bag of up to 10KG in weight. This bag can be up to 55 x 40 x 20cm in size and passengers will need to be able to load this into the overhead locker themselves without assistance from the flight crew. Checked luggage is also available to add for those who prefer to put items into the hold. There are 10kg, 20kg and 23kg bag options available.

However, despite the warnings, one family got caught out at the airport after not checking their bags' dimensions and allegedly were hit with a £400 fee. A poster on Which? Travel's Facebookpage claimed they ended up being given the charge after not checking the rules before their return flight to the UK.

In a statement responding to the claims made at the time, Ryanair said: "People should avoid Ryanair's high fees for oversized bags. They can do so by simply travelling with bags that meet our agreed dimensions. Our sizers are bigger than our permitted dimensions, so if that the bag fits in the sizer, it gets on, if it doesn't, it gets charged."

In a Which? report, its travel team set out a series of guidelines to avoid paying extra costs when travelling with Ryanair. The number one rule is to make sure the bag you bring really does fit into the holder, as gate crew will often check bag sizes. If your bags don't fit into the sizer, you could end up being charged for extra luggage and potentially made to check your bag into the hold.

Don't rely on measurements given by your bag's manufacturer. Get the tape measure out when the bag is packed, as luggage can be bulkier when full, and make sure you include the wheels and folded handle in your measurements.

Ryanair's website warns: "Passengers who bring an oversize bag (over 55x40x20cm) to the boarding gate will either have their bag refused or, where available, placed in the hold of the aircraft for a fee of £/€ 70.00 - £/€ 75.00. You will be required to leave your bags at the aircraft steps, in the gate bag trolley, or as directed by Ryanair agents, for stowage in the hold."

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It also warned that passengers need to ensure they've booked the second cabin bag if they want to bring one, as there's no guarantee it'll be accepted at the gate. "Non-priority customers who bring their 10kg check-in bag to the boarding gate will either have their bag refused or, where available, placed in the hold of the aircraft for a fee of €/£ 46.00 - €/£ 60.00."

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