Chairmen, especially those embarrassed by the share price on their watch, feel obliged to examine any old merger or acquisition idea. But there are limits to what counts as credible and Barclays’ John McFarlane was seriously off-piste if he thought shareholders would be remotely interested in a corporate combination with Standard Chartered.The idea provoked inevitable derision in the City. First, Barclays’ entire strategy for the past three years has been to reinvent itself as a US-UK “transatlantic bank”, minus its former African business. Merging with Standard, which operates almost exclusively in Asia and Africa, would be a U-turn too far. Second, regulators would probably demand substantially bigger capital buffers, thereby negating the appeal of Standard’s Asian deposit base. Third, the potential to rip out costs, banks’ usual justification for big mergers, would barely exist.Barclays’ “exploratory conversations”, according to the FT’s report, were prompted by the perceived need to have a plan B to hand when the unsmiling agitator Edward Bramson turns rough. Bramson’s Sherborne fund has bought a 5.4% interest in Barclays and a confrontation of some form is inevitable becau