Olivia Pennant says she's the laziest woman in Britain. She lives on chocolate and gets a cab to the corner shop. Entering a 26-mile charity trek ... that was an accident.

Olivia's everyday diet comprises cigarettes, beer and chocolate. She rarely eats fruit.

She takes a taxi to the local shop, is a stranger to the gym and has been known to sleep on the sofa rather than climb the stairs to her bedroom.

But the mother-of-two has shocked friends and family by entering a gruelling 26-and-a-half mile charity walk.

She said: "I found myself out of work for the first time in my life with a lot of time on my hands.

"I decided I had to do something. Then I saw a leaflet to take part in the Playtex Moonwalk for breast cancer and I filled in the form.

"They only had 10,000 places and I was sure I wouldn't get one. Then, to my horror, they told me I had.

"The other thing I didn't realise is, I have to do the walk wearing just a bra on top, which should be funny with my 34F breasts.

"I have seen pictures of the event last year and everyone had weird and wonderful decorated bras, so I need to find someone to help me decorate mine.

"My friends are all wetting themselves because I am so lazy and they know what my lifestyle is like.

"I have been offered so much sponsorship money by friends if I even walk one mile, let alone complete the whole thing, because nobody believes I will do it."

Olivia, 36, a former sales rep, has started a training regime which involves bike rides and an occasional short walk.

But she is nowhere near ready for the hike in May.

Exercise videos languish in the corner of her sitting room, some still in their plastic wrappers, and she has had more drinking sessions with her personal trainer than workouts.

She said: "My training diary is full of entries which say how I got up at 2pm, smoked loads of fags and ate a packet of chocolate fingers.

"Then there are entries saying how I put my tracksuit and trainers on, went downstairs to go for a bike ride but changed my mind and went back upstairs to watch TV.

"In another one, I got up with my daughter and walked her to school then came home, meaning to work out - but instead I went back to bed, got up at 2pm and had a fry-up.

"I have been good some days and I am really enjoying going for bike rides on the seafront."

Olivia, of Albany Villas, Hove, said: "When I first moved here, I couldn't walk up the stairs without getting out of breath and I had to stop. It's like a marathon in my own home.

"For the first six months I lived here, whenever I'd had a few drinks, I would just sleep downstairs on the sofa rather than climb all the way up to my bedroom.

"Sometimes I just put on my gym clothes and sit on the sofa because at least it makes me feel sporty.

"I have a theory chocolate fingers are so small that if I eat a whole packet it is only the same as eating two or three chocolate digestives. Also, they are on special offer so I have a whole cupboard full of them."

Olivia hopes the walk will prove to be a turning point in her life.

She said: "I will be 37 this month and I would like to be able to say I have achieved something."

The walk takes place in London on May 11, starting from Battersea Park at midnight.