Possible fossil ID

Found this strange stone while fishing at a man made lake in Northumberland England.

I just thought it was some kind of shell bearing creature, but it became quite the talking point at the pub!

So far, we've had:
"100% a seed pod."
"Looks like a muscle shell to me!"
"Some kind of snail"
But then things got interesting...

"Dinosaur."
"its a claw. You can see the nerve there, and the tip is sharp"
"Close! Its actually a tooth!"

After lots of discussion, noone is sure, so I thought I'd turn it over to you nerd...erm...friends!

What is it?

Where can I get more info?

Help me imgur-kenobi. You're my only hope...