What draws hacks to the other side?

Lesson one: be wary of trusting your old friends. Lesson two: learn that you can no longer laugh at politicians, at least to their faces. These, say Westminster spin doctors, are the things former BBC reporter Martin Sixsmith will recall as he settles in to his new job as Jo Moore's replacement as media-relations adviser to Transport Secretary Stephen Byers.

Sixsmith, who has previously worked for Harriet Harman, is one in a long line of journalists who has "crossed the line" into party politics.

Nick Wood, the Conservative Party's press chief, who worked previously as a political correspondent for the Express and Times, says the move is a culture shock - but an interesting one. "As a reporter I was always intrigued by what went on behind the scenes," he says. "Now I am behind them myself, and it is fascinating to see what is really happening. In a purely professional, journalistic way, that is intriguing and captivating."

In moving from front-of-camera to the shadows of spindom, Sixsmith follows the example of such former BBC colleagues as Lance Price, who became a Downing Street aide in Tony Blair's first term, Emma Udwin, who now works for the European Commission, and Mark Laity, who became a spokesmen for Nato. David Walter, a former ITN reporter and BBC newscaster, notes that although the cliché speaks of "poacher turning gamekeeper", there is "an element of poaching" in spin doctoring just as in journalism. Ex-journos are more likely to know their former colleagues' weaknesses. They can help politicians second-guess the media.

But they have to beware spilling secrets in front of their old comrades. "You can still talk openly to real friends but you have to be certain who they are," says Nick Wood. "Some things you simply cannot tell anyone."

Which is more satisfying: journalism or spin doctoring? "I believe I have more influence now, more chance of getting something in which I believe on to the news agenda," says Walter.

Former hacks understand the broadcasters' technical demands. Andrew Scadding, once a producer with On the Record, is now a Tory Party media officer. "During the election campaign the digital channels, in particular, need updated images throughout the day," he says. Scadding knew he had to provide cameras with photo opportunities not just once a day but every morning, afternoon and evening. "Having worked at the BBC you know what is going to make a story for the different BBC outlets. You know the terminology and the programme editors, too."

The number of journalists moving into politics suggests two things. First, political parties, while outwardly contemptuous of journos, acknowledge that they have a flair for communications many party sweats will simply never acquire. Second, many political journalists are becoming frustrated. As one broadcasterturned-spin doctor puts it: "I felt I was becoming less a journalist than a processor of news."

For the reporters, it can be a mixed blessing to have former colleagues in charge of the information. Yes, they may know better how, in Jo Moore's unhappy phrase, to bury a story. And their adherence to the impartial standards of old Whitehall may be a little lacking. But as former friends they will have a better appreciation of deadlines and they are less likely (with one or two glaring exceptions) to take themselves and their political masters seriously. The relationship between journalists and spin doctors can be conducted at a far more grown-up, streetwise level.

Pay-wise, senior spin doctors do at least as well as Beeb reporters - Sixsmith's predecessor, the unlamented Ms Moore, was pulling in some £70,000; he is said to earn £100,000. But life as a spin strategist may require longer hours. "At the BBC I would be first into the office if I got there at 10am," says Scadding. "Now, there would probably be an inquisition if I got in that late." Nick Wood's working day can often last from 8am to 10pm. "But having been in the political lobby you know all about working late hours," he says.

Last word goes to David Walter. "The internal politics at the Lib Dems," he says, "are a lot less vicious than in the BBC."