Low-cost carriers are a fantastic way to navigate Europe from London. But the trick has been trying to compare their low fares with the major airlines.

Easyjet and BMI, and other usually tease you with superlow prices but then tack on lots of fees for "extras" such as checking a bag, selecting a seat, or purchasing a ticket online with a credit card.

The countless fees mean that a ticket on a traditional carrier like British Airways may seem to be more expensive at first, but after you add in the fees charged by competitors, starts to look competitive—or even cheaper.

Today, TripAdvisor's British site has launched a search tool for flights departing from the U.K.: tripadvisor.co.uk/flights. (This is similar to the tool TripAdvisor has for booking flights within the U.S., which we told you about earlier this year.)

Before you book, the site estimates the fees you'll shell out for flights from the U.K. and throughout Europe. You can compare side-by-side, apples-to-apples what the total fares after all add-ons are, well, added on. There's a currency converter, too.

It includes all of the airlines you might want to fly. That's great news because many of the discount airlines aren't listed on travel sites that you may be more familiar with.

One down side. TripAdvisor doesn't include Ryanair in its searches! Like Southwest in the 'States, Ryanair tends not to participate in online booking engines. Sigh.

The site debuts just in time. This fall, Delta, United, and American have dropped routes and reduced the number of flights they make to Europe dramatically. That makes it smarter than ever to split your trip into separate legs and buy round-trip tickets on different airlines for each leg. Fly an American carrier to a major airport like London, and then hop a discount carrier to fly to your final destination in Europe. (For details, see our post on "The Two Ticket Solution.")

The site also makes it easy to check to make sure that the budget carrier will drop you within easy reach of your final destination.

TripAdvisor doesn't sell the tickets itself. Instead, it directs you to the airline's websites or to Britain's largest travel companies, such as Expedia, Opodo, and ebookers.com, to make your purchase.

Thorough info from SeatGuru means you can look at color-coded maps to see detailed info about each seat, from legroom to noise levels, and pick the best spot to park your bum (as the Brits call it).

Info about the airlines and their main features (such as seatback entertainment options, if any) are also listed when you push your mouse so that the cursor flies over the airline logos in the search results.

EARLIER
Try the two-ticket solution! As U.S. airlines cut their service to Europe, it's a great way to save on fares

Kudos to TripAdvisor for including fees in its new fare search tool