First, for US readers, Dragons Den is like the US show, Shark Tank.
Second, some research shows the product was likely "TV Fix" which is just an antenna.
Apparently, there is a UK law that requires the cable companies to rebroadcast all free channels that the cable company does not have to pay for on a low frequency or low power (or low power and low frequency) band for free. These channels are usually self sustaining and survive on ad revenue and the rebroadcast is vital to getting an audience that justifies the ad revenue. However, these channels also generally broadcast on digital broadcasts as well.