FOUR Olympic medallists found themselves sinking into the Thames after they were brought together for a rather unusual kind of kayaking at the Longridge Activity Centre on Monday for a BBC TV show.

London 2012 stars Zac Purchase, Anna Watkins, Rob Williams and Alex Partridge joined radio DJ Tony Blackburn and a BBC crew in Marlow for a Children in Need challenge to build themselves a cardboard boat for a race down the river.

Zac went solo while Anna and Rob and Alex and Phil Kennedy, from Radio Berkshire and Oxfordshire, made doubles.

Competitors had to build the vessel using only scissors, tape, and bin bags.

Zac, Anna and Rob chose a canoe-like design, but Alex and Phil decided to build a raft.

Zac said: "I am on my own so I did some research to figure out the best design, but most of my research said that cardboard boats are very likely to just sink."

After 45 minutes of hard work and creative thinking, Zac ended up with quite a unique canoe featuring an umbrella to protect him from the rain that had been pouring down all day.

Anna and Rob had what they thought to be a strong canoe with places for two to kneel on, and Alex was confident his raft was very likely to float.

Above all, the ex-Olympians were just glad to join the fundraising event.

Alex said: "It’s good to see that despite the recession people can still manage and are willing to give way money for charity. "And investing in children it’s about investing in the future."

Anna said: "I used to come out here to train and always watched the children having fun. Now it’s our time to have fun and probably get wet."

Anna’s forecast was spot on.

As the race started, Alex, assisted by Phil, took the lead with his raft which, incredibly, did not sink.

The other competitors went down quickly.

Zac sank immediately and his umbrella was hopeless under water. Anna and Rob could hardly get into their canoe.

At the end, Alex was the winner and the others had to swim dragging their boats across.

Tony, Phil and the Pudsy, from Children in Need, were at the finishing line to salute the brave athletes.