The TV stations are steadily in need of new faces and the new ones picked have had some positive display in some way. Deep and exact knowledge from engineers and professors aren't neccesarely the best presenting towards the livingrooms across the nation, however it's practical to have such co-hosts.
Guy Martin certainly has his followers due to his status as motorbikechamp and IoM racer. As a motorbike entusiast I loved to see the IoM documentary about Guy Martin: Closer to the Edge and without having seen it I've noticed another TV-seria with Guy Martin and a houseboat.
Such programmes is made for the average TV spectator and is doomed to be neglected by people with deeper knowledge - Just like the movie Red Tails, based on the Tusgee airmen story: Good entertainment, but not for flybuff's.
Try seeing the programme with the houseboat and re-judge the appearence of Guy Martin out of that!