Well, it's not strictly true that Prof Roger Wotton from UCL (a.k.a. the Godless College of Gower Street) made that claim; he is rather a demonstration of it. He has apparently published an article in a UCL magazine all about how angels cannot fly. This claim alone is simply foolish. Given that angels are wholly spiritual beings, they can neither fly nor not fly; asking the question "can angels fly?" is about as meaningful as asking "what colour is next Tuesday?"
On closer examination, it turns out that he claimed that angels, as they are portrayed in art especially painting, are anatomically incapable of flight, due to underdeveloped shoulder and chest muscles. He then goes on to say that the fairies with gossamer wings so favoured by sentimental Victorian illustrators can't fly either!
Some of Professor Wotton's approach might simply be a certain robust scepticism, which is no bad thing in a scientist as the Climategate scandal has recently shown. Perhaps he might be motivated by scorn for New Age angelology and all its works & pomps. However if he is seriously suggesting that the sort of Angels described here are the sentimental anthropomorphic figures of angel cards, he really ought to think again. Better still, he might keep in future keep to areas about which he knows something. After all even a fool, if he will hold his peace shall be counted wise: and if he close his lips, a man of understanding.
Lastly, if you want a good imaginative picture of what an encounter with an angel might be like, check out John C. Wright Esq and his shortest of short stories.