Television presenter Davina McCall has described how her arduous charity exploits for Sport Relief last month left her in a “very dark mental place”.

Davina, 46,  suffered an emotional meltdown during her fundraising efforts for BT Sport Relief Challenge: Davina – Beyond Breaking Point, due to be aired on BBC1 on Thursday 20 March, ahead of Sport Relief 2014 on Friday 21 March.

The mother-of-three embarked on a week-long 500-mile run, cycle and swim from Edinburgh to London, raising more than £750,000 for good causes and shedding plenty of tears along the way.

Davina said the sheer physical exertion resulted in her “sobbing my guts out”.

“It was like somebody had opened the floodgates and I let out every single bit of grief that I had.

“I kept crying every day… I think I was just so tired that I had no defences, and I was just sobbing at everything. “

She added: “I’m normally a chipper person. If you’re in a positive state of mind you can cope with pain and jolly yourself along, but I had moments when I went into a very dark mental place.”

The former heroin addict admitted she doubted herself throughout the challenge, but persevered after seeing the work her charity ordeal would help fund at a Sport Relief project in Africa before setting off.

She also said the memory of her half-sister, Caroline, kept her going. Caroline died in 2012 after being diagnosed with cancer. ”I felt like she was with me [on the challenge] a lot.”