Holidaymakers are being warned not to be lured in by exceptionally low flight prices without doing a little bit of extra research. There are plenty of budget airlines out there, such as easyJet with flights this summer from £27 or Ryanair advertising flights from £30.

However, one thing these airlines, and many others, are known for doing is ramping up the cost with extra charges.

These extra fees have been referred to as “hidden costs” by experts from Quotegoat.com. Michael Foote, CEO of the travel insurance comparison, has said that missing these “hidden costs” is one of the “biggest mistakes” Britons make when booking a holiday abroad.

“More and more airlines, not just the budget ones, are adding fees for checked luggage that can range from £20 for a short-haul flight and can be as much as £150 for long-haul flights,” he explained.

Most long-haul airlines will allow you to take a checked bag as part of your ticket price unless you have selected a hand luggage-only seat. With budget carriers, both hand luggage and checked bags can come at a price.

Ryanair, for example, only permits passengers one small hand luggage item for free. Anything more than that and you’re looking at anywhere from £6 to £60 depending on what luggage you want to take and whether you purchase it online or at the airport.

“Airlines will also charge as much as £50 for choosing where you sit,” added Michael.

Even some of the top-name airlines in the world have started adding on excess fees. For example, customers who book an economy seat with British Airways will need to pay for seat selection if they want to lock in their exact seat number before check-in.

Check-in with British Airways opens 24 hours before departure, at which point seat selection in certain rows becomes free. However, for customers who want to sit in a specific part of the cabin, this can be risky.

British Airways’ website states: “The cost of selecting a seat varies depending on the type of seat and the cabin you’re travelling in.”

British Airways has now removed the price list from its website, but when they did publish guideline costs, according to Head For Points, starting prices varied from £7 to £62 depending on which cabin you are sitting in.

Of course, these prices may have changed now and are likely to vary depending on route, availability, cabin and dates of travel. With that said, British Airways, like most big-name airlines, will always aim to sit groups together even if you don’t pay for a seat. The only exception to this is Ryanair, who say that seats are randomly allocated.

Michael said: “When booking flights and accommodation within a specific budget, be mindful of additional costs by carefully comparing prices, including those you may not see until checkout. While it might seem like you’ve found a bargain initially, once you’ve factored in all the extras, you may need to go back to the drawing board.”