* UK's Cameron sees 2011 as year to deliver trade deal
* PM warns against return to 1930s-style protectionism (Recasts with new quotes)
By Keith Weir
SEOUL, Nov 11 (Reuters) - British Prime Minister David Cameron said on Thursday that long-running efforts to achieve a global trade deal must be successfully concluded next year to give the world economy a shot in the arm.
Britain argues that completion of the so-called Doha round could boost the global economy by as much as $170 billion and is vital when interest rates are at record lows and many Western countries are curbing government spending.
"It's got to be something we achieve next year. It's an international embarrassment that we haven't completed this trade round," he told a business summit on the sidelines of the G20.
"We need to make this deal bigger in order to make this deal better in order to push it through faster," he added.
The talks were launched in late 2001 but have been deadlocked for two years, largely because of differences between the United States and big emerging economies such as India, China and Brazil.
Commentators say a deal needs to be wrapped up before attention in the United States turns towards the 2012 presidential election.
Cameron, who took office in May after ousting Gordon Brown from power, said that the G20 must avoid a return to the protectionism of the 1930s as the consensus fostered by the 2008 credit crisis frays. Brown played a prominent role in the G2O's response to the crisis.
Cameron said the G20 was not in what he called a "heroic phase", but argued that it was not losing relevance.
"One of the main purposes of this G20 should be to show we're going to fight protectionism in all its forms," he said.
"We're going to fight trade barriers, we're going to fight beggar-my-neighbour policies. We're going to fight (against) currency wars. We're going to fight competitive devaluations."
Britain is backing efforts to create a free trade area for Africa as a whole, Cameron citing the example of South Korea which has transformed its economy over the past four decades through heavy trading in goods. (Editing by Tomasz Janowski and Alex Richardson)