Nick Bell, the executive creative director at JWT London, is to leave Sir Martin Sorrell's troubled agency after almost three years.

Mr Bell's departure is the latest in a string of management changes that have so far failed to get JWT's struggling London office back on track.

JWT London's performance, which saw it lose £60m in client business in 2005 and at least the same again last year, is an important issue for Sorrell's WPP group.

It has been dented by the struggling performance of WPP's United London, which lost the £75m Sky business to WCRS in November.

JWT London replaced chief executive Simon Bolton, who had run the agency for five years, at the end of 2005 after a poor year that saw the loss of the global Persil business to Bartle Bogle Hegarty.

The agency also missed out on winning big accounts such as the £47m Sainsbury's and £60m British Airways advertising business.

Early last year, Alison Burns, a former president of Fallon New York, was appointed as chief executive to spearhead a turnaround. However, the revival has largely failed to materialise to date.

Last year the agency was hit by the JWT worldwide network losing its place on the $1.5bn (£763m) global ad account for Reckitt Benckiser.

The Reckitt Benckiser global account loss saw JWT's London office relinquish £28m in ad business for brands including Cillit Bang, Dettol, Lemsip, Harpic and Disprin.

JWT London closed the year with the loss of the £47m UK Vodafone ad business to BBH, which handles the mobile phone company's international branding work.

There have been some notable successes, including last summer's win of Smirnoff's £20m alcopop business, Smirnoff Ice, from BBH. JWT already handles the rest of Smirnoff's brands.

The agency moved in October to shore up its top-level management by hiring the BBH deputy chairman, Guy Murphy, to be global planning director.

And earlier in the summer JWT's London office hired Hugh Duthie, the chief strategic officer at TBWA\Chiat\Day New York, to be its head of planning.

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