RUBBISH!   LOL!   IT'S A QUOKKA - A WALLABY LIKE CREATURE THAT LIVES OFF ROTTNEST ISLAND ABOUT FIVE MILES OFF PERTH IN WESTERN AUSTRALIA - I WAS OUT THERE IN '78.  A DUTCHMAN LANDED ON THE ISLAND AND CAUSED HYSTERIA BY SAYING THE ISLAND WAS OVERRUN BY GIANT RATS.  

People go to the island specifically to feed them although you're not supposed to because this encourage real rats. They're quite harmless.  How one came to be in the UK is anybody's guess.  Probably smuggled in as a joey and grew too big.  That's as big as it'll get.