On the order confirmation page click on 'Redeem a Promotion Code' and enter ARROW211 in the voucher field.
Please note: this is a 6 episode science show featuring the Wallace and Gromit characters.
Wallace and Gromit's World of Invention is a BBC One science show featuring the animated claymation characters Wallace and Gromit, made by Aardman. The BBC said in a press statement that in the series, "Wallace will take a light hearted and humorous look at the real-life inventors, contraptions, gadgets and inventions, with the silent help of Gromit. The series aims to inspire a whole new generation of innovative minds by showing them real, but mind-boggling, machines and inventions from around the world that have influenced his illustrious inventing career."
All credit to Halcyondaze for posting the voucher.
Don't forget Quidco/TCB.