Many other foreign creatures are now lurking in our fields and woods, so it's quite possible that popular pet-shop fare, such as bull or king snakes, could have slipped out while their owners were not looking. Pythons and boa constrictors, beloved by exotic dancers, could probably survive fairly well on rats, mice, voles and frogs. But Steve alleges that a far more menacing species has taken up residence.
Trout fishing on the river Tawe in the Swansea Valley, Marsh says that he was accosted by a 7ft cobra. "The only time I've seen one before was in an Indiana Jones film," he said (which may make you have some doubts about his identification). "It was 10 times more frightening in the flesh," he added, though he didn't mean it literally. In the true spirit of the dedicated angler, Marsh did not rush off screaming. He simply crossed the river and carried on fishing, though he claimed: "Even then I didn't feel safe."
You might wonder how Marsh retained the presence of mind to measure the snake despite his terror. But anglers are masters at this sort of thing. Listen to fishermen and you will notice how often they say: "I lost a 10-pounder," without ever seeing the fish. It's a great talent.
Still, perhaps we should not be so sceptical. My brother-in-law, a senior accountant and the most sane person I know apart from myself, swears he saw a panther while walking in Devon. And two other anglers claim to have had narrow escapes as the Welsh cobra "reared up out of long grass and prepared to strike".
Herpetologists may be baffled by this uncharacteristically aggressive behaviour. Cobras, like most snakes, prefer to slink away when danger threatens. One remote possibility, assuming you're prepared to accept the cobra scenario rather than the more probable discarded bicycle inner- tube, is that the snake had a nest nearby and was protecting its offspring. A more likely explanation, however, may be found inside the nearby Pontardawe Inn.
The landlord, Peter Clayton, obviously concerned that his customers could curl up and dai, says: "It has been the talk of the pub. We are advising our customers not to go out looking for it. The police must be treating it very seriously. They had a helicopter sweeping up and down the river bank." The version I read had chief inspector Phil Bevan saying: "The description of its markings and its hooded, rearing action of the neck make us pretty certain it's a cobra - and a big one."
You have to admire the thorough training those boyos get in the Welsh force. My local bobbies couldn't tell a hamadryad from a fer-de-lance. You might also wonder how even eagle-eyed Welsh coppers, peering into the valleys from hundreds of feet up, are going to spot a snake hiding in long grass. You may even suspect that the snake owes its parentage not to a paddy field near Bombay but to several pints of Evans' best.
If you're thinking of taking a fishing holiday in Wales this summer, take note that the cobra is said to be patrolling between Pontardawe and Godre-r-graig. Determined to risk your life in the quest of Welsh fish? Take the advice of reptile expert Kevin Greedy, who is helping with the search. He says: "If anyone sees it, they should back away slowly, avoiding eye contact."
You could also note that the snake is thought to be an escaped pet, though quite what sort of person keeps a 7ft killer cobra for fun escapes me. Should Tiddles threaten you, a better bet may be to sway from side to side and hum one of those catchy little sitar numbers tapping your foot on your creel at the same time.
Once the snake's inside, you can fish away without interruption. And you might be able to make a few bob from it at Saturday markets.