Calling the only Conservatives response partisan is not neutral. Both parties see the other as partisan, and themselves as acting in the national interest. Furthermore, the Conservatives have made their exact reservations about loss of sovereignty quite clear. Don't use phrasing that implies the contrary.

'the influence of the right-wing and American-friendly press' makes it sound like all the press meet that description, but their are not many who consider the Guardian to be either. Also, do papers dictate their readers opinions, or copy them? Since that's highly debatable, don't assume a position. 

'fear of "loss of sovereignty" — a fear not apparently present on the continent' Scare quotes are partisan, and there are polls showing 40-50% opposition in France, which is on the continent.

Shorter paragraphs are more readable on screen.