Sarah Wyles bought her parents two EasyJet tickets to Barcelona as a Christmas present. Unfortunately what should have been a cheap weekend away ended up costing them more than £400 extra after their return flight was cancelled.

The airline said there was no chance of getting them on another flight for three days because everything was fully booked. They were offered £50 in hotel expenses between them and asked to rebook their flight via a fax number. No one from EasyJet offered the couple any help or advice.

Luckily Wyles's parents met another couple who rang their daughter. She booked them EasyJet flights to Liverpool the next day for £150 each. The £50 offered by EasyJet didn't even cover their extra night's stay at a cheap hotel and they had to fork out money for taxis (the last airport bus had gone), food and the train ride home from Liverpool. It took them another day to get home.

'My parents will never fly Easyjet again. If it's going to cost them all that extra money they might as well go with British Airways who will at least treat them properly,' said Wyles, from London.

If Wyles's parents had flown to Barcelona with BA and the flight had been cancelled the airline would have arranged both a hotel and transport to and from the airport. BA's extensive network would also have meant that the couple would have had more chance of getting home the next day, even if it was via another of BA's destinations in Europe.

So is it a case of you get what you pay for? Wyles paid£120 for her parents' tickets, substantially less than two BA tickets, which would have cost between £131.40 and £580.40 return per person. But not every low-cost airline passenger ends up picking up a bargain, and they still get the same service.

Zoë Sargasso, from London, was delayed by five hours on her way home from Carcassonne, southern France, with Ryanair last month. She paid £200 for her ticket, which she bought five days before the flight. 'The fact that you can pay that and then are charged £7.50 for a beer and an inedible sandwich is not satisfactory. The planes were uncomfortable, very dirty and there was no light in the lavatory. If I had paid the advertised fare of £46 all these things would be bearable. If they charge these fares they should be providing the same service as all the other airlines.'

Unfortunately it doesn't work like that. Like all airlines, the no-frills carriers have a range of fares. EasyJet, for instance, charges anything from £40 to £360 return from London Luton to Barcelona. Around 10 per cent of its seats are sold at the lowest quoted fare, and those are usually booked months in advance.

An EasyJet spokeswoman said: 'People must understand that it is not going to be financially viable for us to carry everyone for £60 return. We have a scale of fares - that is how we make our money.'

Simon Evans, chief executive of consumer watchdog the Air Transport Users' Council (AUC), says the term 'low-cost airline' is sometimes misinterpreted by the public who believe they will always get a low fare. 'The no-frills airlines' costs are lower because most of their bookings are taken over the internet, they don't have in-flight catering so they don't have to employ so many cabin crew, but all those factors don't always translate into low fares.'

There is, however, still a big difference between the fares offered by no-frills airlines and those sold by their scheduled rivals. 'You can still get a £35 ticket to Rome. You are not going to get that with BA or Alitalia,' Evans added.

Scheduled carriers such as BA and Bmi British Midland are fighting back now. BA is slashing fares on 71 short-haul routes across Europe and is scrapping the Saturday night stay rule. Bmi has introduced one-way fares and also dropped the Saturday night stay restrictions. Even the charter airlines are getting in on the act. Britannia Airways is now offering flexible one-way fares to destinations such as Palma and Malaga while MyTravel is launching its own low-cost carrier.

Despite the new competition, the popularity of the low-cost airlines is showing little sign of waning.

And although most of us are simply shopping for the lowest fare, it's worth noting that the level of service offered does vary even among the no-frills airlines. So read on to find out how they measure up against each other and against a traditional scheduled carrier when it comes to customer service.