British Airways has taken a kicking lately. Fined hundreds of millions of pounds for price-fixing, vilified for its inability to unite thousands of passengers with their luggage, and so on. But at least the airline can pride itself on one thing: its fares online are competitive. Indeed, BA.com proudly declares: “We promise that if you find exactly the same BA flight cheaper on another UK website, we’ll refund the difference.”

What most of its passengers don’t realise, however, is that they may be able to find the same flights cheaper using an American-based website.

In fact, one reader, Roger Gibbens of Hitchin, Hertfordshire, saved 30% off the BA.com price on a flight from Rome to London by buying from the US site Orbitz.com. “I gave my address in the UK, paid with a UK credit card and confirmed afterwards with BA that the booking was all in order.”

So we did some digging. We compared British Airways fares from Rome to London on a series of dates, and consistently found prices lower on US websites. On October 6, BA.com had a flight from Rome Fiumicino to London Gatwick for £67.42. Orbitz.com , an American price-comparison site, quoted £38.31. But even that wasn’t the best deal available. On the aptly named Cheaptickets.com , we found the same BA flight for £35.78 – saving 47%.

This is all very well if you need a one-way ticket originating from Italy, but does it work if you’re booking flights out of the UK? Well, yes, it does.

Let’s say you planned to fly from Heathrow to Fiumicino on October 6, returning a week later. At BA.com the fare was £143, but the same flights were available at Orbitz for £116.43.

And the same applies to BA’s transatlantic fares. At Cheaptickets.com, the lowest fare from London to New York on August 28, returning on September 4, was £295.84, only £1.26 cheaper than BA.com. But BA’s fare was only available for passengers willing to return on a daytime flight out of Newark.

Those who wanted one of the 10 other flights BA operates from New York to London that day – including the redeyes – pay more. Indeed, other flight times quoted by Cheaptickets. com would have cost £419.10 at BA.com, a 41% premium.

So, where’s the catch? Will you get the same level of consumer protection and customer service if you buy from an American website? What would happen if the website went bust?

Neither Orbitz.com nor Cheaptickets. com is likely to go under anytime soon. Both are part of Travelport, a multinational giant that also owns more familiar brand names such as Ebookers and Travelbag. Orbitz was valued last year at more than £375m.

And BA says that once you’ve got your booking reference, it’s all the same. “There are no implications for travellers [if you book through an American website]. You can still check in and manage your booking online.”

So why the discrepancies? British Airways admits that it’s a case of one fare for the UK market and another for the American one: “We price differently in different markets, based on the state of the market and on what our competitors are doing.” The airline also claimed that taxes are higher on some routes if booked out of the UK. On Heathrow to JFK, the difference is about £15, it said.

This sort of tactical pricing is now outlawed within the EU, but not across the Atlantic. BA admits it may be forced to rethink its policy. “We will look at this in the future as part of our overall pricing strategy,” it said.

Are other airlines playing the same game? Virgin Atlantic said: “We do sometimes bring out promotional fares to stimulate demand in different countries, particularly in the USA at the moment.”

We couldn’t find evidence of tactical pricing on routes operated by Virgin Atlantic and BMI. There were discrepancies, but only marginal ones, but it’s clearly worth keeping an eye out.

Nor was it always cheaper to book British Airways flights through American agents. In many cases there was little difference between the fares, and, in a few instances, BA even undercut the US sites. But not by much.

The fares were found on August 7; the conversion rate used was £1 = $1.974

How to do it

THE SUREST way to find the lowest fares is through an American comparison site such as Sidestep.com , Kayak.com or Mobissimo.com . These will display a range of fares for a given route on a given date, and direct you to the booking pages of the relevant agents. To be sure you don’t miss a better deal, run the same search on a UK comparison site such as Travelsupermarket.com or Traveljungle.co.uk.

If you’re booking a flight within the EU on an American site, you’ll need to tick a box to confirm that you are an EU resident. Your fare will be quoted in US dollars. Once you have a booking reference, you can log on to the airline’s own website and manage your booking in the usual way.

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