This pitiful young Great Northern Diver surely won't make it to adulthood. The images show clearly the fishing line caught inside its' mouth, to such an extent that it is ripping the gape. Images below also show the line has tightened round the back of the neck. I also have a suspicion that the line is tangled round the left wing as a long sequence of shots showed that it cannot stretch the wing.
In the past, there has been an outcry about auks being tangled in nets in Carbis Bay - it looks very much like the issue is still with us.