Top EU Net contributors for 2013 (including rebate and subsidies) -
1st: Germany €13.8bn
2nd: UK €8.6bn
3rd: France €8.4bn
4th: Italy €3.8bn
Source:
http://english.eu.dk/en/faq/faq/net_contribution which is a Danish Government website.
The UK's contribution is higher than what Spain and Greece combined receive, and that's just the EU budget
Access to the London financial markets is of huge benefit to the rest of the EU, just as access to the EU markets is of huge benefit to the UK, in fact it would be better for the EU if France or Italy left (or in fact any other country bar Germany), than it would be for the UK to leave.