In my backpacking heydey in the Eighties, you could almost guarantee your fellow travellers would have a Lonely Planet or a Rough Guide stuffed into their rucksack. They were as essential a piece of travel kit as your passport, a rite of passage to pore over on the train or in the youth hostel, to lend and borrow and to fuel a conversation at the bar.

Lonely Planet had been churning out books since Maureen and Tony Wheeler put together Across Asia on the Cheap on their kitchen table in 1973. It was the era of the jumbo jet, when baby boomers were spreading their travel wings, helping to fuel demand for information on getting there, the best places to stay and above all, how to do it on a budget.

It is hard these days to find a destination the books do not cover. And it is not just books - in the Nineties, Lonely Planet started up its website, with its famous Thorn Tree travellers’ forum, plus a television series.

No wonder it enjoyed such a heady growth curve: from printing just 1,500 copies of that first book, Lonely Planet sold 3.24 million books over the past 12 months in the UK, the US and Australia.

But now, the internet is changing the guidebook industry dramatically, so although it is coincidental that the news of Lonely Planet’s sale comes just days after the announcement that Rough Guide’s co-founder Mark Ellingham is moving on, it is not entirely surprising.

With more travellers going online, the guidebook market is starting to drop – last year sales dipped more than 2 per cent, falling 5 per cent in the first half of this year, according to the Travel Publishing Year Book.

As Tony Wheeler, speaking from his home in Melbourne, Australia, told me: “The business is no longer just about guidebooks. The digital side will at some point be larger than the print side.”

Recent years have seen a move from destination-specific guides to niche areas, such as luxury hotel guide Mr and Mrs Smith and the Hedonist’s Guide series.

Lonely Planet responded with its own niche publications - one of its most popular was a series on travel photography. Recently, it has also produced city guides with Nokia mobile phones. And this year, it launched Haystack for online hotel bookings (on the basis that it was easier to find a needle in a haystack than a good hotel), as well as Pick and Mix guides, whereby chapters of different books can be downloaded from the internet for multi-destination travellers.

But it is just the start of how the internet is revolutionising travel information, and Mr Wheeler recognises that his and his wife’s strengths remain in traditional book publishing and travelling - they still spend about six months a year on the hoof.

“The digital side isn’t our bag as much,” he said. “We thought if we were going to do it properly, we had to do it with someone else and the BBC popped up.

“There will still continue to be a good market for guidebooks, but it will change.”

Times recommends

• Travel advice: what to do if your flight is disrupted
• Top 10 unmissable events in 2010
• Seven spa breaks for January