Now, I'll be honest - I still think that this may have been an elaborate April Fool's Day prank, and others have suggested this as well. Even if that is true, however, it managed to dupe the BBC, which is pretty scary.
The individual who was interviewed on the program, Brian J. Ford, has a website where he discusses the supposed merits of aquatic dinosaurs, etc. I was just going to laugh and blow the whole thing off, but it occurs to me that his supposedly "difficult" questions might actually pose some interest to readers. So, here is my quick debunking of his list. Enjoy.
"a) How dinosaur limbs could otherwise have borne such weight
(up to 100 tonnes)"
-- Short answer: easily. Longer answer: bone is much stronger in axial compression than in bending or torsion. Sauropods, in particular, had columnar limbs, so the bones were loaded almost purely in axial compression. Their long bones were also almost solid compact bone at midshaft. The failure stress of compact bone in axial compression is 170 GPa, which for comparison, is nearly 5x the compressive failure stress for concrete. Not only could sauropod limbs support their weight, not a single sauropod known to date was at the mechanical limit for the group. It's also worth noting that the 100 tonnes estimate is pretty outrageous. Mike Taylor (an expert on sauropods, specifically) estimates Giraffatitan to have weighed in at 23 short tons in life. That is among the largest known sauropods. So it's a bit puzzling where the other 80+ short tons are coming from. Perhaps sauropods were composed largely of metal.
"b) Why they would expend such a large amount of metabolic energy holding tails erect
(There are no tail drag marks in the fossil footprints; there are for crocodiles)"
--"Why" is presumably because of mobility and balance. What I think he really means is "how", to which the answer is that holding tails erect is not very energetically expensive when much of the weight support is done by tension. Besides, plenty of animals hold parts of their body upright for long periods of time. We hold our entire trunk, upper limbs, head and neck erect.
"c) How they maintained their steady body temperature without the cushion of a huge body of warm water (Isotope analysis shows they maintained a constant body temperature and no reptiles evolved a mechanism to do so)"
--Vertebrate animals are mostly water to begin with; large animals have naturally high thermal inertia as a result (this leads to the possibility of so-called "gigantohomeothermy" for very large ectothermic, organisms). Even more damning, however, is that Ford has forgotten basic physics here: unless the water was the temperature of the animals, or greater, they would lose heat over time while submerged. Given that homeoendothermic animals (i.e. "warm-blooded") can be 90+ degrees or more resting temperature, that is some awfully hot water. Oh, and "reptiles" have evolved endothermy at least twice (see: mammals and birds - the latter, being dinosaurs, likely inherited some endothermic traits from the very sorts of animals Ford implies could not possibly have been truly endothermic).
"d) Why the abundant fossil footprint are proportionately comparable
(They'd have sunk up to the armpits were they standing on dry land)"
--The depth to which an animal sinks is a product of the shear imposed on the substrate, not simply total mass. This depends on the stress on each foot, as well as duty factors and substrate conditions. In short, there is no reason to think that a large dinosaur would sink appreciably deep on dry land. Elephants, for example, do not leave footprints much deeper than those of humans.
"e) Why they claim that Spinosaurus - and a host of similar dinosaurs! - simply dipped their heads beneath the waves (Their snout glands are like those of crocodiles; clearly they spent most of their lives in water)"
--"Host" here is about three or four, depending on who you ask. In short, while spinosaurids have cranial features associated with aquatic feeding, the postcrania typically lack any major aquatic adaptations. Hence, the current best conclusion is that they hunted from the shoreline.