The invisible thread that links assets as diverse as gold, bank stocks, the Japanese yen and government bonds would be yanked sharply by Brexit, an event the Bank of England said on Thursday risks "adverse spill-overs to the global economy".

With global interest rates and bond yields the lowest on record, central banks running low on crisis-fighting tools and the post-2008 economic recovery flagging, that thread could quickly unravel, with serious consequences for all markets.

GRAPHIC: reut.rs/1OtYjrc

So why will the will of one country's people in one referendum have such a profound impact on global markets?

The answer is partly how interconnected global markets are, and partly timing – the world economic cycle is already very long in the tooth and central banks have far fewer options open to them after nearly a decade of extraordinary policy support.