British retailer Tesco has said Philip Clarke will step down as the CEO of the company and will be replaced by Unilever's chief of personal care, Dave Lewis, effective on 1 October.

Clarke will continue to be available to support the transition until the end of January 2015, the company noted. He will also remain chairman of the company's joint venture with CRE in China until that date.

"Having guided Tesco through a substantial re-positioning in challenging markets, Philip Clarke agreed with the Board that this is the appropriate moment to hand over to a new leader with fresh perspectives and a new profile," Sir Richard Broadbent, chairman of the company, said in a statement.

During his term, Clarke has worked hard to "set a clear direction and re-position Tesco to meet the rapid changes taking place in the retail market", Tesco said.

"Having taken the business through the huge challenges of the last few years, I think this is the right moment to hand over responsibility," said Clarke, who replaced Sir Terry Leahy as CEO of the company in 2011.

The company noted that Lewis brings a wealth of international consumer experience and expertise in change management, business strategy, brand management and customer development.

"The Board believes that with Dave's leadership Tesco will sustain and improve its leading position in the retail market," Broadbent said.

The management shakeup comes as the company is facing challenging market conditions.

"Current trading conditions are more challenging than we anticipated at the time of our first quarter interim management statement on 4th June," the company said.

"The overall market is weaker and, combined with the increasing investments we are making to improve the customer offer and to build long term loyalty, this means that sales and trading profit in the first half of the year are somewhat below expectations."

Tesco added that its recent investments, conditions in the overall market and possible steps to improve customer offer during the remainder of the year will be crucial for its full-year outlook.

Tesco shares closed at £2.85 on 18 July.