It is a section of pyrite nodule in the suggestive shape of a sharks tooth. A typical megalodon from the Naze would have a polished appearance, potentially due to being re-deposited from Miocene deposits and the colour stained from the iron pyrites in the London Clay (below the Red Crag). Keep looking, megalodon teeth turn up several times a year at Crag sites and you may get lucky.
Nice megalodon tooth, UK fossil guy. I agree with your ID (Riks piece deffinietly isn't a tooth.)
There is also a megalodon tooth from this location on a website 'discovering fossils'. If you google 'English megalodon tooth' it will turn up on the first line. It is very water worn, but it is still very rare for that location (I think sand sharks are more common in that location.)