Eighty days: that is all that remains until 2008. An excellent time, then, to follow in the footsteps of Phileas Fogg and Michael Palin. British nights are longer and darker, the days are shrinking fast. Leaving the country to head south, east or west has plenty of appeal, with the extra benefit that travelling in the Muslim world becomes easier from today – this weekend is the end of the holy month of Ramadan, with celebrations across the Islamic world. And for those able to travel in the next two months, long-haul flying is a buyers' market from now to mid-December.

So what's to stop you clicking around an airline's website to find a good deal to Africa, Asia, Australasia or Latin America? Work and family commitments, perhaps. But even if you can overcome those obstacles, think twice before booking direct with an airline: cutting in the middle man, in the shape of a travel agent, confers many advantages.

First, you could pay less by going through an agent than by booking direct with the airlines. A decade ago, that was a racing certainty for long-haul flights; occasionally a call to check fares with, say, Qantas might elicit a whispered recommendation from a helpful individual that "you'll pay less through an agent".

Even though almost every long-haul airline sells direct through its website, they recognise that many travellers prefer to use a specialist agent. And since the UK is the world's most competitive aviation market, the airlines often have to offer agents seats at fares that undercut direct-sell prices. Airlines also appreciate the volume of business that agencies can deliver: when ailing Alitalia sought to fill thousands of empty seats to Australia, it chose Airline Network to sell the lowest-ever fare between London and Sydney: £352 return (a deal that has long expired – unlike, surprisingly, the airline.)

On a trip from Heathrow to Singapore via Dubai, the best fare Emirates offered me on its website was £815 return. A friendly human being at Trailfinders sold me exactly the same flights for £40 less. This helps to explain why the firm remains the biggest long-haul agent in Britain, despite a web presence most kindly described as rudimentary.

Unlike machines, staff in agencies can unlock extra value in your ticket. With years of accumulated expertise, they can suggest stopovers or add-ons that are available free or at negligible extra cost. An example: if you fly to Australia with Malaysia Airlines, the airline offers a "nearly-free" side-trip within Malaysia. You can fly to Borneo for a short stay in Kuching or Kota Kinabalu for little more than the cost of a couple of nights at a hotel on this wild and wonderful island.

For anything with an extra degree of difficulty, such as a round-the-world trip, you should certainly consult an expert such as Travel Nation: on a multi-stop trip via the South Pacific, this Sussex-based company saved me hundreds of pounds by taking advantage of a little-known airpass loophole.

Another benefit: when buying online you usually have to pay in full at the time of booking, with tickets being issued straight away. After tickets have been issued – even the paperless, electronic version – harsh airline rules usually apply, generally making it very expensive if not impossible to make subsequent changes to the date or route.

By booking with an agent, you can usually pay only a deposit, with the balance due at a later date. This confers the security of a firm booking, but with the flexibility to make changes for little or no charge up to the time tickets are finally issued. And when things go wrong, you have a human contact you can talk to (or, these days, email) to sort the problem out. Every week I receive calls and emails about customer service issues with various online providers, from travellers whose moods range from plaintive to furious .

By talking your way around the world, rather than clicking, you could even have a more comfortable trip.

Here's how. While air fares have never been lower, planes have never been fuller. Average "load factors" – the percentage of seats filled are in the high 70s worldwide, and on many routes to and from the UK the figure is in the 90s. Good news for the environment, because it means planes are flying less inefficiently. But if you happen to be crammed into 28B on an Ethiopian Airlines 757 (yes, the middle seat in the non-reclinable row next to the loos) you will crave an empty seat next to you.

Research by Boeing suggests that passengers rate an unoccupied adjacent seat as equivalent to an extra eight inches of legroom. In other words: it's a mini-upgrade. So the secret is to identify the less full flights. And that is where a travel agent comes in.

While travellers can access airlines' reservations systems either direct or through online agencies such as Expedia and Opodo, you find out nothing about the loading beyond whether or not a seat is available. In contrast, specialist travel agents have access to much more information on the status of a particular flight. An agent should be able to tell at a glance, at least at the time of booking, if a plane is likely to be full to the brim or wide open. With 11 flights a day, each way, on the 12-hour haul between London and Hong Kong, it pays to seek a plane where you can stretch out.

www.trailfinders.com; 08450 58 58 58; www.travelnation.co.uk; 0845 344 4225