Metronet said that John Weight was to step down as chairman and chief executive as the company "needed to accelerate change" on its Tube renovation programme, a public private partnership (PPP) deal.

He will be replaced as chief executive by Andrew Lezala, the Jarvis chief operating officer, who has become the second director to quit the troubled contractor in five weeks.

The shake-up came as the London Transport Users Committee demanded a meeting with Tube bosses over the poor performance of Metronet and Tube Lines, a second contractor.

Brian Cook, the LTUC chairman, said: "The time has come to ask formally whether the level of disruption is such that Metronet and Tube Lines can be said to be in breach of their contracts."

Last week Bob Kiley, the London transport commissioner, described Metronet's performance as "completely unacceptable". MPs, in a report last month, said that the £15 billion, 30-year PPP contracts awarded to Metronet and Tube Lines were failing to deliver value for money.

Metronet's members - which include WS Atkins, whose chief executive, Keith Clarke, will become the Metronet chairman - said today that they were "committed to meeting and exceeding" their PPP obligations.

Mr Lezala's departure from Jarvis comes 18 months after he joined and six months after he was promoted to chief operating officer, a period in which he played a major role in the restructuring which prevented the company collapsing under the weight of its debts.

The revamp included the £146 million sale of Jarvis's stake in Tubes Lines.

Alan Lovell, the Jarvis chief executive, said that Mr Lezala had played "an important role in helping the group through difficult times".

Mr Lezala, noting Jarvis’s survival through a "critical and challenging" time period, said: "The opportunity to be involved in the improvement of the Tube infrastructure is extremely attractive for a Metro railway specialist such as myself."

Mr Lezala, a former Bombardier executive, joined Jarvis as head of the contractor’s rail division, on which the company has focused revival efforts, and played a key part in rebuilding relations with Network Rail after the Potter Bar rail crash three years ago.

He was considered a candidate for Jarvis chief executive until Mr Lovell was appointed to the role last year.

Mr Lezala's departure follows the resignation last month of Alastair Rae as finance director.

Jarvis shares stood 2.25p higher at 17.25p in afternoon trade.

• In a separate statement, WS Atkins said that it would hit profits hopes despite a slowdown in the rail and road markets.

  The company said that its performance had been hit by delays to Network Rail and Highways Agency programmes.

  However, it added: "The outlook for 2005-06 for the group's core markets is good despite the anticipated short-term challenges in the rail market."

  WS Atkins shares stood 35.5p higher at 665.5p in afternoon trade.

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