Ok, there are bigger ones out there, but "Barry" was living in a marine aquarium at Newquay's Blue Reef Aquarium in Cornwall, England. Unknown to the aquarists and visitors Barry sneaked in, probably with a shipment of "live rock" (I really don't like that misnomer) a common invasion vector for bristle worms, and ruled the roost as it were, growing to a remarkable 4 feet long. Barry fed on the corals and fish of it's aquarium. After being coralled by aquarists, Barry now has his own tank at the aquarium where everyone can revel in the beauty of marine polychaetes!
The original Daily Mail posting stoops to the, unfortunately too familiar, derogatory epithet of "Monster". They also point out repeatedly that the bristles can be quite a pain and even cause numbness if you get a little too personal with them. I guess it's fortunate that they didn't comment on the hyper cool, but horror movie inspiring, evertable pharynx and the jaws which look awfully like giant fangs.
Personally I would love to see Barry firsthand.