Chuka Umunna has dramatically quit the Labour leadership race, citing "very real concerns and worry about this bid's impact on those close to me".
The shadow business secretary announced he was withdrawing from the contest to succeed Ed Miliband, just days after declaring he would be a candidate.
In a statement, the frontrunner to head the party's rebuilding after last week's general election defeat said he had underestimated the level of scrutiny to which he and his family would be subjected.
"As a member of the shadow cabinet, I am used to a level of attention which is part and parcel of the job. I witnessed the 2010 leadership election process close up and thought I would be comfortable with what it involved.
"However, since the night of our defeat last week, I have been subject to the added level of pressure that comes with being a leadership candidate.
"I have not found it to be a comfortable experience.
"One can imagine what running for leader can be like, understand its demands and the attention but nothing compares to actually doing it and the impact on the rest of one's life.
"Consequently, after further reflection I am withdrawing my candidacy."
Mr Umunna, who said he hoped to remain a member of the shadow cabinet, apologised to those who supported his bid and said he had always harboured doubts about whether he was ready to step up to the biggest role.
"I apologise to all those who have kindly supported and encouraged me to do this and for disappointing them. I know this will come as a surprise to many but I had always wondered whether it was all too soon for me to launch this leadership bid - I fear it was.
"Most importantly, I continued to have very real concerns and worry about this bid's impact on those close to me.
"I intend to carry on playing my full role as a proud member of our shadow cabinet taking on the Tories.
"I also hope to play a leading role in Labour's campaign to keep the UK in the EU during the forthcoming referendum, which is absolutely crucial. Most importantly, I will as ever continue to serve the area I know and love - the Streatham parliamentary constituency."
At the weekend the politician was pictured arriving at TV studios for an interview hand in hand with his girlfriend, who had previously remained out of the public eye.
He said he had decided before the campaign started that he would pitch for the leadership if Mr Miliband failed to steer the party back into power.
"I dearly hoped Labour would win the election and it was a decision I would not have to implement. I also thought I understood the scrutiny and attention a leadership contest would bring."
The unexpected withdrawal means there are now four declared candidates: shadow health secretary Andy Burnham; shadow home secretary Yvette Cooper, shadow international development secretary Mary Creagh; and shadow health minister Liz Kendall.
Under a timetable drawn up by the party earlier this week, nominations for leader close on June 15. Members and supporters who sign up by August 12 will be entitled to vote and the result will be announced on September 12.
Shadow education secretary Tristram Hunt said he was "interested in the leadership" of the party while on BBC Question Time but stopped short of declaring his candidacy.
In full: Chuka Umunna's statement
"Shortly before the election campaign, I made the decision, in the event that Labour was defeated and a new Leader was to be elected, to stand for the leadership of the party if there was a desire in the party for me to do so.
"I dearly hoped Labour would win the election and it was a decision I would not have to implement.
"I also thought I understood the scrutiny and attention a leadership contest would bring.
"As a member of the Shadow Cabinet, I am used to a level of attention which is part and parcel of the job. I witnessed the 2010 leadership election process close up and thought I would be comfortable with what it involved.
"However since the night of our defeat last week I have been subject to the added level of pressure that comes with being a leadership candidate.
"I have not found it to be a comfortable experience.
"One can imagine what running for leader can be like, understand its demands and the attention but nothing compares to actually doing it and the impact on the rest of one's life.
"Consequently after further reflection I am withdrawing my candidacy.
"I apologise to all those who have kindly supported and encouraged me to do this and for disappointing them. I know this will come as I surprise to many but I had always wondered whether it was all too soon for me to launch this leadership bid - I fear it was.
"Most importantly, I continued to have very real concerns and worry about this bid's impact on those close to me.
"I intend to carry on playing my full role as a proud member of our Shadow Cabinet taking on the Tories. I also hope to play a leading role in Labour's campaign to keep the UK in the EU during the forthcoming referendum which is absolutely crucial. Most importantly, I will as ever continue to serve the area I know and love - the Streatham parliamentary constituency."
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