New drawing challenge for Lizzie Mary Cullen

London illustrator Lizzie Mary Cullen is set to decorate a classic British telephone box over a 24 hour period in Covent Garden, supporting the charity Childline

24-hour drawing challenges are becoming a speciality for London-based illustrator Lizzie Mary Cullen. Last year she took on Pendurance, vowing to draw 50 different locations in London during a 24 hour period. She did it, and so this year she's teaming up with BT and sponsor First Direct on a charity project that will see her spend Monday 18 June decorating a classic telephone box in Covent Garden. The non-stop creative marathon will be in support of the 25th anniversary of Childline.

Go down to Covent Garden and you'll see her hard at work giving the replica phone box - originally designed by Sir Giles Gilbert Scott for the Silver Jubillee of King George V - a makeover. Other creatives producing ArtBoxes in London include Malcolm Garrett, Ted Baker and Rian Hughes.

An image inspired by a bike ride through London

"This is really exciting as it's for a really great cause," explains Cullen. "There's going to be over 80 replicas of Gilbert Scott phone boxes all over London. The ArtBoxes are sponsored, made into interesting art installations and then auctioned off to raise money for ChildLine’s 25th anniversary. I was approached to do the First Direct ArtBox."

Something Cullen has discovered taking on drawing marathons is that it makes her hungry. "Seriously, during Pendurance I was eating everything that wasn't nailed down. But I guess being on your feet non-stop eats into my energy levels. I actually ate the gherkin out of my Big Mac ,I was that hungry. I hate gherkins," she says.

Detail from the Pendurance challenge artwork, created last year.

However it also benefits her creativity. Getting out of the studio and into the wild, she feels free of the normal constraints - explorative and experimental. She adds: "Usually my line work is very rigorous and controlled, but in this type of situation I find myself focusing a lot of on the feel of the work, rather than the look of the line. This method is very effective on a bigger scale, and has a lot more impact."

Lizzie Mary Cullen has drawn numerous London landmarks. This is Somerset House.

She'll be tweeting about her creative process during the challenge, so follow her on Twitter if you can't get down there. You should also check out her tutorial, where she demonstrates how to film your own drawing projects using stop motion to create an impressive video of your work taking form. And, as she explains, she can't wait to watch her ArtBox decoration take shape on Monday. "I think it's going to be an awesome 24 hours! It's a challenge, and I love pushing myself to the limit. I'm really excited about getting stuck in, and watching the Art Box take form," she concludes.