Student Alex Putnam thought of a cheeky way to promote a sustainable crop - by running in a G-string made from it.

Alex, 20, entered the Sussex Beacon half-marathon on Sunday with his modesty covered in just a thong made of hemp.

The Brighton University undergraduate is now planning to race in Australia and in the London Marathon leaving even less to the imagination.

Although hemp used to be a very popular clothing material, it grew out of favour during the industrial revolution as machinery to process cotton improved.

Later, many governments banned it because of its associations with drugs but in the Nineties, new strains were introduced which had no narcotic value.

Alex, who studies geography, said hemp was a very useful crop which could be grown across the world.

He said: "This is nothing to do with cannabis. I'm promoting hemp because of its environmental benefits. You can use it to fuel cars, for food and clothes.

"The original idea was to run on my own through Brighton in a hemp G-string and gain publicity that way. But then I decided to enter the half-marathon."

On Sunday, Alex lined up alongside 1,600 other runners and the thong clearly caused him no discomfort as he ran close behind the race leaders.

He said: "In Brighton I just had a tiny T-shirt to keep me warm but in the London Marathon I will be going bare-chested."

Charmagne Steedman, who works at the Hemp Shop in Gardner Street, Brighton, said: "We specially made the thong at Alex's request as we mostly sell T-shirts. It was based on a thong he had run in before so we didn't have to measure him.

"The shop has been here for about two years. There are quite a lot of people in Brighton who are ecologically aware. They don't want to wear cotton because it is a huge polluter.

"We tend to add a little cotton to garments to soften them but try to use organic items as much as possible.

"We also sell food and cosmetics but this is the first underwear we have sold, although we are starting a line in ladies' underwear soon."