While Ken Collins has gone live with this observation there is at least one multi-author publications in press as well a variety of other observations (including video) from west Wales, the east coast and Dutch coast supporting this observation. 

Ken Collins ‘It’s one of the big mysteries in my career as a marine biologist. Something lurking in the seas off Britain has been chomping away at local porpoises and none of the usual suspects fit the bill. Now scientists have finally identified the cuddly culprit. I first became aware of the attacks on porpoises – beakless, smaller relatives of dolphins – as I run the UK shark tagging programme and am often asked to comment on possible sightings. In both 2010 and 2011 I was sent pictures from the Norfolk coast of porpoise carcasses with a considerable amount of tissue bitten away.  common assumption was that these were due to shark attacks. However none of the photographs of the wounds showed the characteristic punctures caused by the multiple rows of shark teeth, such as displayed by human victims of shark attacks.’

To read more click here:

http://theconversation.com/grey-seals-in-the-dock-over-porpoise-murder-mystery-34690