Coypu are extinct in England after at least two waves of extensive trapping which occured in the 1960s then the 1970s-1980s. Over 70,000 coypu were trapped in East Anglia, the main stronghold, and they were declared officially extinct at the end of the 1980s (although a few individuals were still knocking about in the early 1990s.) They were farmed through the 1930s and early 1940s for fur but escaped quite readily (along with mink who were also in these farms) and by the 1950s both species were established in the wild.

I do get called out to sightings of coypu a couple of times a year but as these animals were the size of a small dog and their burrows and feeding signs absolutely enormous there is no chance they could escape notice in a pond or river. The sightings always end up being extremely large brown rats. However even brown rats wouldn't be the size you describe. Could you have seen a muntjac deer crouching down for a drink? This would be brown, large but nowhere near as large as a Roe Deer or Fallow Deer, have prominent 'tusks' and is very likely to be found in the habitat you suggest. I can't think what else you could have seen.

On the subject of Muskrats, these are not a UK species, being Native to north America, and are approximately the size of water voles with similar habits and ecology. They are the main prey item of American Mink which is why mink are so adept at hunting water voles.

Hi Darren, am really sure it was not a deer. It had extremely large front teeth, that's why I was so convinced I had seen a beaver. I have never seen an animal like this, the only thing close would be a rat; but if this is a rat, then i'm leaving Essex. It was enormous! bigger than my dog who is about 6kg.

Just to clarify, it was in the woods that begin as you walk towards Arlesford, past the sailing club. About 20m in there is a dew pond on the lefthandside, which is overgrown with brambles and hedging. I heard a rustling and looked to see something, no more than 5m away, down on top of what looked like pile of branches in the water. The animal looked straight at me, it was brown with a longish coat. It was at this point I turned around and went.