Bank of England policymaker Adam Posen said on Monday he is more worried about economic stagnation than inflation or deflation, and that central bankers need to guard against repeating the mistakes of the 1930s.

What I'm worried about is stagnation, said Posen, when asked what concerns him more over the next three to five years. It's not about inflation or deflation, it's about very large, real shocks bumping the economy up and down around a relatively austere, low-growth path, Posen said.

Speaking at the Council on Foreign Relations in New York, Posen said he fears that 50 years from now, policy will be viewed in the same way the Depression era is now, which he called a major deflationary mistake.

If we repeat the mistakes of the past and prematurely tighten or insufficiently loosen, whatever you do on fiscal policy, whatever you do on financial regulation will be overwhelmed by that mistake, Posen added.

Posen, known for his dovish views, said that economic stimulus efforts by central banks only become inflationary if central banks are unwilling to withdraw those measures when the time comes, and there is nothing to suggest that will be the case.

The Bank of England restarted its quantitative easing program in October with a plan to buy 75 billion pounds of government bonds, on top of the 200 billion pounds of purchases it made in 2009 to 2010.

Meanwhile, the U.S. Federal Reserve has bought more than $2 trillion (1.3 trillion pounds) in long-term securities to keep borrowing costs down and spur the U.S. economic recovery.

Last week, Posen wrote an op-ed urging the European Central Bank and the Fed to buy significant amounts of government bonds to help boost their economies.

(Reporting by Leah Schnurr; Editing by Padraic Cassidy)