Neither accountants nor politicians are especially popular at the moment, but that still does not make them a good mix. A rushed rule change, due to come into effect today, has been produced by the US Financial Accounting Standards Board, under pressure from Washington. The way forward is not a series of piecemeal revisions.

The change by FASB would apply to first-quarter results, which should be published over the coming weeks. Depending on how it is used, it could make a significant difference to how banks present their numbers. It would make some banks’ books look better than under the present regime because the banks would be able to value more of their holdings using their own models rather than markets, where the markets for particular types of holdings, such as complex financial instruments, are deemed illiquid.