We had a huge influence right up until push came to shove and then we had none. I agree we can't become great - isolation or not; I believe that isolation isn't on the table either - next few weeks excluded. The reality is that France and Germany shafted the UK publicly and conclusively during the euro crisis, they also shafted the Greeks - but I'm not Greek so that's less of a problem for me. Remember also that they removed an Italian government and installed a technocrat. Yet lots of people seem to have forgotten that and either don't care or can't bring themselves to see the reality of the situation.
We aren't in the Euro zone and were never likely to be.