You've seen the adverts, you've surfed the net and you've managed to find that cheap flight. But before you click on 'buy now', take a few minutes to check every detail of your booking agreement. Otherwise, you may find that the attractively cheap top line price has been transformed into an expensive overall total, often considerably more costly than a scheduled flight from your local airport.

Over the last few years, the advent of budget operators offering progressively lower and lower fares to European destinations has revolutionised air travel. Many of the best offers are only available over the internet, but this presents a problem: frequently the websites advertise a bottom line price for the flight itself exclusive of 'hidden extras' such as tax, making it difficult - and occasionally impossible - to work out the total amount you will be required to pay. In addition, prices quoted are often for one-way flights only, and return flights may be considerably more expensive, or unavailable.

Budget air operators are able to reduce expenditure by cutting indirect costs. The main means by which they reduce expenditure include using cheaper departure and destination airports and providing a no-frills, no-meals service, with no pre-assigned seats or express check-in facilities. However, although this benefits the operators, it can often prove awkward and costly for passengers.

So, if you don't want to get stung by hidden costs and extras, pay particular attention to the following:

Departure Airport:

Most low-cost airlines- such as easyJet at Luton and Buzz and Go at Stansted - operate from a base airport around London. However, it can be difficult and expensive to reach these airports. It takes over 40 minutes to reach central London, using the Stansted Express, and the cheapest return fares on offer at the time of writing range from £19.50 and £35. Passengers for Luton who wish to take advantage of the return Thameslink rail fare of £8 have to book at least two months in advance and easyJet does not list prices for non-booked tickets.

Destination Airport:

Many low-cost companies also use minor, or secondary, airports as their destinations: Buzz, for example, does not fly to any major airport. Some of these airports do not have the same levels of passenger service as you might expect from a major city airport, and many are a considerable distance from city centres. Ryanair's Paris base, Beauvais, is 35 miles from the centre of the city, and Charleroi, another of its airports is 37 miles south of destination city Brussels. It is essential to find out the costs and frequency of public transport between these bases and city centres before confirming your booking.

Flight times:

Typically, the cheapest fares are often only available off season, and on early morning, late evening or night flights. Again, it is crucial to confirm if, and when, transport is available from your destination airport. There is no direct public transport, for example, from Prestwick (Ryanair's Glasgow base) for late night arrivals, meaning passengers wishing to reach the city have to travel the 30 intervening miles in a taxi.

Taxes, Fees and Charges:

Often taxes, fees and surcharges increase the first fare quoted considerably by the time you reach the point of purchase. All companies levy various charges, ranging from a surcharge to cover additional insurance costs since September 11, to what easyjet calls a 'Barclays fat cat' charge of £5.50 for using Luton airport. Always check these out carefully.

Luggage:

Low-cost flights increasingly service popular Mediterranean beach resorts in summer and Alpine ski slopes in winter. But before you pack your surfboards, skis and snowboards, check you won't be hit by yet another extra cost. easyJet levies a £25 return charge for surfboards and, while bmibaby offers an additional 10kg for golf clubs and skis, this is "subject to space". Bikes and canoes are defined as outsized items, so specific charging conditions apply to them.

Go has recently introduced an extra 10kg allowance for golf clubs and other sports related equipment, which should benefit golfers jetting off to the Costa del Sol or the Algarve.

Extras:

Make sure you have enough spare cash to cover in-flight snacks and drinks. All low-cost airlines charge for refreshments, prices vary and only Go lists the tariff on its website.

If you're planning a long term stay and want to take your cat or dog with you, try a scheduled airline. None of the low cost operators carry live animals, or participate in the passport-for-pets scheme. Neither do they transport dead bodies, should you be unfortunate enough to suffer a bereavement during your holiday.

And finally, always make sure you check-in on time. All low-cost operators enforce strict time limits and any passenger failing to reach the gate at least 30 minutes before flight time will forfeit their seat and will not be eligible for refund, credit or free transfer.

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