GBBO's Martha Collison takes on the #BelowTheLine challenge

Martha was the youngest of last year's GBBO contestants, and is now raising money for Tearfund.Twitter / @ChartersSchool

Known for her succulent cakes, Martha Collison didn't win the competition but did win the hearts of the nation when she appeared on TV's Great British Bake Off at just 17.

She is now about to take her "A" levels, revising hard for exams through a time when most of us might need more carbs and calories than ever before to get through the stress.

On a recent food blog, she wrote about the joy of loaf cakes: "I always feel the need to even-off the end to make it perfectly straight after having a slice. This often means having another one. And another one. It's too hard to stop!"

But now she has had to stop, because this is the week that Martha Collison is attempting to get through the week on just £5, or £1 a day, for Live Below The Line's #belowtheline challenge.

The aim is to persuade people in affluent western nations to join voluntarily the 1.2 billion people forced to live on less than £1 a day, and raise funds for the charities helping to alleviate global poverty through sponsorship.

Martha, a committed Christian, is doing #belowtheline for the relief charity Tearfund. Other celebrities doing the challenge include Maddy Hill, who plays Nancy Carter in EastEnders, who is living on £1 a day for Action Aid. The Bishop of Bath and Wells Peter Hancock and his wife Jane are also doing the challenge for Send a Cow.

Dame Judi Dench is among those making supportive comments on Twitter.

Other tweets contain imaginative recipes and photographs of cost-free uses for traditional and cheap vegetables such as broccoli, potatoes and carrots, along with eggs, tinned peaches and sliced bread.

But for someone whose passion is cooking and cakes, #belowtheline is a particular challenge. On her blog, Martha writes: "I love food and appearing on GBBO has only made me more obsessed with it."

Just how much she really does love food is apparent from her recent description of one culinary exercise: "This is one of those cakes that reminds you of all that is good in the world. Sticky chocolate sponge infused with strong brewed coffee, topped with espresso butterscotch icing and crushed roasted hazelnuts. I would say it's great to enjoy with coffee, but that's not true; it's coffee and cake all in one delicious package."

All her creative skills will now be dedicated to more ascetic cooking styles.

"I will be living on £1 a day to raise money to help eliminate poverty and see a better future for millions of people. Seeing poverty first hand in Cambodia earlier this year opened my eyes to the harsh lifestyle that millions of people call reality. Meeting children at risk of trafficking, of which poverty is the root cause, has made me even more passionate to stop this horrific crime. We can help stop it, so please give generously."

In her Tearfund blog about Cambodia, she wrote in solidarity with the thousands of children every year who are trafficked across borders. During her time there she traced the route across the border into Thailand, to support Tearfund's anti-trafficking campaign No Child Taken.

"To be able to trace the steps of girls my age who have had a very different, horrific life, and raise awareness of the work is truly powerful. But you don't have to travel halfway across the world to be able to have an impact - whether it's marching through the high street with your mum, or walking the county border with your whole community, everyone can help raise money to end the horror of modern slavery."