I'm not a twitcher or a birder (I'm not much of a naturalist either), but a walk along the Thames on Wednesday evening (and backstreeter is right, the Abingdon waterfront does take some beating) I noticed something unusual swimming on the river and ventured back this morning to see if I could find it.
I eventually caught up with it as it swam under the Abingdon bridge and towards the upper reaches hotel and my suspicions were correct, it was Red Crested Pochard:
Consulting the RSPB Handbook of British Birds, there are only 50 breeding pairs in the UK and there are some migrants from Europe. But as there didn't seem to be any others on the Thames, it is highly probably that this one escaped from captivity.
Back in January, Martin posted a comment asking if there could be red crested pochards on the Thames and although ten moths late in answering, I can confirm Martin, you were right.