What is Quantitative Easing and Why has it been used?

Quantitative easing is a policy introduced by the Bank of England to pump [to date] £375 billion into the economy. It works by the BofE purchasing government bonds (known as Gilts) off private and institutional investors which increases the price of government bonds, thus lowering the yield* and making it cheaper for the government to borrow. When first used it was seen as a form of unconventional monetary policy and was used because the central tool in a monetarists pocket – the use of interest rates to stimulate demand – was ineffective. [...]