LONDON (Reuters) - Calling himself a  proud saboteur  of the Brexit process, Britain s Liberal Democrat leader Vince Cable on Tuesday appealed to opponents in all parties to put aside differences and fight a divorce from the European Union. The fourth-largest party with 12 representatives in the 650-seat parliament, the Liberal Democrats are hoping to become the lightning rod for any rise in anti-Brexit sentiment as Prime Minister Theresa May s government edges closer to leaving the EU in March 2019.   Cable, an economist who was business minister in the 2010 to 2015 Conservative-Liberal Democrat coalition government, has redoubled his party s criticism of the decision to leave the EU since becoming party leader in July.  I want our party to lead the fight against Brexit,  Cable said in his address to the party s autumn conference. He called for a new referendum, describing Brexit as a looming disaster.  In the real world, we have yet to experience the full impact of leaving Europe. But we ve had a taste of what is to come in the fall of the value of the pound,  Cable said. Sterling fell by as much as 20 percent against the dollar in the months after the June 2016 EU referendum. It has recovered around half those losses, in part thanks to increasing expectations of an interest rate hike to ease inflation, but the pound is still 9 percent down on pre-Brexit levels.       Foreign exchange dealers are not point-scoring politicians, they make cool, hard, unsentimental judgments. Quite simply, that Brexit Britain will be poorer and weaker than if we had decided to stay in Europe,  Cable said. He also said the government was relying too heavily on its relationship with the United States to help it adjust to life after Brexit, criticizing U.S. President Donald Trump as  volatile, and dangerous and an apologist for religious and racial hatred.   Opposition to Brexit has been emboldened after May failed to win a clear mandate for her exit strategy at a snap election in June. She lost her majority in parliament but kept power thanks to a deal with a small Northern Irish party. Cable said Britons had a democratic right to a second referendum once the final terms of the Brexit deal become clear.  At the end of these tortuous divorce negotiations, the British public must be given a vote on the outcome,  he said.  But polls show little sign of a radical shift in public opinion against Brexit. Polling firm YouGov said a significant proportion of the 48 percent who voted against Brexit now thought the government had a duty to leave. Only 27 percent of Britons want to reverse the decision, they said. Cable, whose centrist party went from junior coalition partner to near extinction in the 2015 election, made only small gains in the June election having set out the party s stall as the most pro-EU party in British politics. Cable has previously said he expects dissatisfaction with Brexit to grow as the negotiations develop, and called for opponents from all parties to come together to oppose the divorce.  We have got to put aside tribal differences and work alongside like-minded people to keep the Single Market and Customs Union, so essential for trade and jobs,  he said. 