Britain would lose influence if it were to leave the European Union, the Vice-President of the European Commission has said.
Speaking in Cambridge, Viviane Reding said that a UK outside the EU "would have to live with the rules decided on by the other EU countries".
Ms Reding said talks of renegotiations and referenda "distracts from the real issue".
"Finding more solutions like the ones [found for the banking and financial sector] is what we should all be focusing our energy and creativity on."
The 1.7 billion euros (£1.4 billion) fines for eight major banks imposed by the European Commission for rigging benchmark interest rates is to be ploughed back into the EU's budget, says ITV News Business Editor Laura Kuenssberg:
Proceeds from bank fines go back to EU budget
The European Commission said it is "determined to fight and sanction" rate-rigging cartels formed by some banks.
Vice president of competition policy Joaquin Almunia said:
Today's decision sends a clear message that the Commission is determined to fight and sanction these cartels in the financial sector.
Healthy competition and transparency are crucial for financial markets to work properly, at the service of the real economy rather than the interests of a few.
The sanctions - the first from the European Commission on rate manipulation - are the highest yet for European anti-trust enforcement.
Barclays is immune from a potential €690 million (£573 million) penalty after the bank blew the whistle on the Euribor cartel.
The Euribor is the euro area equivalent of the London interbank offered rate (Libor).
RBS fine is 391 million euros - latest in a long line of costs for past bad behaviour
RBS, Barclays, Deutsche Bank found to have acted as a 'cartel' over euro interest rates
Eight banks fined total of 1.7 billion euros for market rigging - ouch
Eight major banks have been fined a combined €1.7 billion (£1.4 billion) by the European Commission over interest rate-rigging.
The European Commission is expected to announce more fines for banks over the rate-rigging scandal, as ITV News business editor Laura Kuenssberg writes:
Hear euro banks fines for market rigging out at 11.30 in brussels - told some banks braced for up to 800 million euro penalties
The European Commission is set to fine a group of banks a record €1.7 billion (£1.4 billion) for rigging interest rates, Reuters reported, citing a source.