The extraordinary clash at the Federal Reserve between Jerome Powell and Donald Trump entered new territory on Wednesday when the outgoing US central bank chairman said he would remain on as a governor – and the president lashed him with another insult.

Powell said that while his term at the head of the Fed was ending May 15, he would exercise his right to remain on the board “for a period of time to be determined”.

Powell appeared concerned about the Fed maintaining its independence in the face...