Are there any safety concerns around 1.4GW flowing through a cable surrounded by salt water? I’m entirely uneducated in the ways of zap juice, but that sounds like a recipe for spontaneous electrocution if that cable breaks anywhere.
The power cable operators don't want to waste any energy and will have power monitoring systems at least at both ends, so much as with a fusebox at home, I'm sure that the cable would be switched off very quickly if that happened. In addition, the power would be dissipated close around the source of the breakage by the (not insignificant) electrical resistance of water. Since the North Sea is about 100 metres deep, the only victims in such event would be fish and other seabed creatures. I don't tend to chew power lines, though, so don't worry about me.
I'm not a physicist but I would imagine it dissipates quite quickly due to some inverse square law.
Think about how lightning exists, and you'll see why this is not an issue.