Big guns roll into the global currency war

London - If 25 countries cutting rates since the start of the year wasn't proof enough, this week's warning from Janet Yellen about the dollar's strength confirmed that the world's top central banks are fighting a currency war.

The scale of global easing has been the big surprise for investors this year. On average an interest rate has been cut somewhere in the world once every 2.85 days, and everybody's been at it.

From the ECB with its 1 trillion euro QE bazooka, China, India and Russia in emerging markets, to Denmark and Switzerland where rates are now so negative that it would be cheaper for anyone with serious money to rent a vault and some heavies with machine guns than to keep it at the central bank.