In this paper I examine the effect of introducing an account-based central bank digital currency (CBDC) on liquidity insurance and monetary policy implementation. An asset-exchange model is constructed with idiosyncratic liquidity risk, in which one type of agents require currency and/or CBDC to consume while the other type of agents can use any assets to trade. There arises a liquidity insurance to distribute assets efficiently by type. Since central bank reserve accounts are accessible by the public directly, the large excess reserves (LER) in a floor system can make it difficult to separate the types under private information. Therefore, raising the interest on reserves in the floor system can reduce the aggregate liquidity excessively, and the equilibrium allocation with the LER can be suboptimal.

This paper examines the outcomes for changes introduced by the UK Coalition government in 2010. The Office for Budget Responsibility (OBR) is generally regarded as a success, and should become a permanent part of fiscal policymaking. The form of the primary fiscal mandate, involving a five-year rolling target, appears to be a sensible way to shape fiscal decisions when monetary policy is able to stabilise the economy. Unfortunately it was introduced, along with a five-year programme of severe fiscal consolidation (austerity), while the economy was in a liquidity trap. The OBR estimates austerity reduced GDP growth by 1 per cent in both 2010–11 and 2011–12, and monetary policy was unable to offset this. For the Liberal Democrats a misreading of the Eurozone crisis may have been responsible for this mistake, but for the Conservatives this mistake appears to derive from an unconventional view that the liquidity trap is unimportant.