Close-Up: Live Issue - No sign of slowdown in turnover of top marketers.

Churn rates have a negative impact on brand strategies. Emma Barns finds out why.

Mike Moran hit the headlines last week when he exited as the worldwide director of marketing and strategy at Thames Water, a post he had held for just 18 months. Meanwhile, Zoe Morgan announced her defection from HBOS to the Co-operative Group (after 15 months) and it emerged Simon Waugh was leaving Centrica.

And that was just last week. Orange, the BBC, BT and Sony PlayStation have also experienced upheaval recently as their respective marketing directors - Jeremy Dale, Andy Duncan, Amanda Mackenzie and David Patton - either departed or moved on through promotion.

So what is the effect on agencies and how much does it damage a brand's consistency? Each time a marketer moves, uncertainty is felt by the agencies of the new and previous client company. Agencies, naturally, fear a review.

Andrew Harrison's first step when he moved from Nestle to Muller earlier this year was to call a pitch. And Jerry Wright promptly reviewed out of McCann Erickson when he arrived at Birds Eye last summer.

But even if the new client is not necessarily plotting a pitch, he or she will be targeted aggressively by a stream of hungry new-business directors.

They pour over Ammo, a weekly list of outgoing marketers, in search of fresh opportunities. For instance, the rumours surrounding the prospect of reviews at Orange and Sony, which both have new marketing heads, are reaching fever pitch.