Lord Brown's Statement:
"For the past 41 years of my career at BP I have kept my private life separate from my business life. I have always regarded my sexuality as a personal matter, to be kept private.
"It is a matter of personal disappointment that a newspaper group has now decided that allegations about my personal life should be made public.
"Legal documents have been disclosed today containing allegations about me and my personal life.
"I wish to acknowledge that I did formerly have a four-year relationship with Jeff Chevalier.
"He has made these allegations about me and our relationship to Associated Newspapers, publishers of The Daily Mail, Mail on Sunday and Evening Standard.
"The allegations are full of misleading and erroneous claims.
"I deny categorically any allegations of improper conduct relating to BP.
"The company has confirmed today that it has found no such wrongdoing.
"My initial witness statements, however, contained an untruthful account about how I first met Jeff.
"This account, prompted by my embarrassment and shock at the revelations, is a matter of deep regret. It was retracted and corrected.
"I have apologised unreservedly, and do so again today.
"These allegations will result inevitably in considerable media attention for both myself and BP. What matters to me is BP, what we have achieved during my tenure and the bright future ahead.
"I have therefore informed the Board of BP that I intend to stand down as group chief executive with immediate effect, rather than retiring at the end of July.
"This is a voluntary step which I am making to avoid unnecessary embarrassment and distraction to the company at this important time.
"I have spent my entire working life with BP, and want to thank everyone for their dedication, loyalty, support and hard work in creating one of the worlds finest companies.
"I shall not be commenting on my personal issues further. I wish to pursue my personal life in private."