Now is the time for European supporters to make themselves heard, Lib Dem South East MEP Catherine Bearder said today.
It comes after David Cameron last night vetoed EU-wide treaty changes aimed at resolving the Eurozone crisis, claiming they were not in the UK's interests.
A fresh deal setting out tougher budget rules will now be drawn up by Eurozone countries with the UK and Hungary frozen out of talks.
Catherine said: "Today's decision is a disappointing setback. British jobs and growth depend on a healthy neighbour across the Channel… that has not changed.
"And my fear now is that we will lose the opportunity to affect decisions which could have a deep impact on our own economy."
She added: "As a Liberal Democrat I remain a passionate supporter of Europe.
"The Coalition Government must ensure the UK continues to work closely with our EU partners to ensure Britain remains at the heart of these debates, not on the fringes.
"It is time for those of us who support Europe, who welcome the freedoms and rights it has guaranteed us, to stand up and be counted."