Barclays, Britain's third largest bank, formally confirmed today that Paul Idzik, its chief operating officer, will leave during the second half of the year and will not be replaced.

A Barclays spokesman declined to comment on whether Mr Idzik will receive a pay-out.

Mr Idzik was not immediately available for comment. He has not disclosed if he has secured a new role.

He said in a formal statement: "I now look forward to identifying and pursuing my next challenge."

"I have enjoyed myself enormously at Barclays over the last nine years and believe that we have made tremendous progress in transforming the organisation so that it better serves the needs of its customers and its shareholders."

A former ranked tennis player, Mr Idzik has been a controversial figure at Barclays, best-known for vaulting the security gate at the entrance of the bank’s Canary Wharf headquarters to test its security in the wake of the July 7 London bombings.

His departure is also likely to ignite further speculation about tensions between Mr Varley and Mr Diamond, since the latter lost out to the British banker in the fight to become chief executive of the bank in 2003. Mr Idzik is a key ally of Mr Varley

Barclays is at pains to point out that the Mr Varley and Mr Diamond have worked closely together for some time.

Mr Idzik, who is a member Barclays' executive committee, does not sit on the board of directors.

His decision to leave is thought likely to have been influenced by the failure of Barclays to win a takeover battle with Royal Bank of Scotland for ABN Amro, the Dutch bank.

Mr Idzik, an American and former management consultant, is thought to have told Mr Varley in January that he was preparing to move on.

Senior staff were informed of his plans to step down yesterday afternoon.

Mr Idzik, previously a partner at Booz Allen Hamilton, the consultancy, was hired by Barclays in 1999 to advise on the restructuring of the bank’s underperforming investment banking business BZW.

BarCap emerged, under the control of Bob Diamond, a former Morgan Stanley banker. Mr Idzik was chief operating officer of BarCap before Mr Varley appointed him chief operating officer of the entire bank in 2004.

Mr Varley said today: "Paul has played a key role in help us achieve this [restructuring]. It is what I brought him in to do and that part of our work is substantially complete. As such, Paul has decided that this is the right time to look for his next challenge.

"I would like to thank him for the considerable work, energy and enthusiasm he has provided to Barclays over the last decade and in particular the counsel and support he has given to me.

"I will miss him greatly," he said.

Barclays is also coming under scrutiny after the announcements in the past two weeks by Royal Bank of Scotland and HBOS of multibillion-pound rights issues. The bank has refused to rule out a rights issue but is thought to have told staff that it would consider all other options, such as managing its exposure to risk, slowing its growth or increasing profits, before a capital raising.

Barclays is scheduled to deliver an interim management statement on its first-quarter trading on May 15.

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