This BBC article suggests that EU wants to exclude us because they do not trust us and our security.
That is quite insulting. They rely heavily on us for security information and intelligence.

We are told that the legality of the move is being investigated.

Also, "Graham Turnock, chief executive of the UK Space Agency, said early feasibility work was under way into a UK system, which he said would cost a "lot less" than Galileo, thanks to work already done and "British know-how and ingenuity".
http://www.bbc.co.uk/news/uk-politics-43891933