For our money this is a dolphin, here's why:
1. No tail, white sharks tails are vertical, if you can see the dorsal on this critter you should be able to see the tail.
2. This story was brought to you by a U.K paper-home to the guys who brought you last month's White shark in Wales.
For those of you who subscribe to Occam's Razor...yeah you're looking at it.
"Pluralitas non est ponenda sine neccesitate"