Last year was a bumper year for mergers and acquisitions. Recovering prospects and relatively low price-earnings ratios made the takeover arena alluring: the global volume of deals looks certain to have passed the $4.3 trillion record of 2007. Among the new giants are Shell-BG, Heinz-Kraft, Pfizer-Allergan and monster brewer AB InBev-SAB Miller; bonuses reaped by London M&A bankers will fund basement diggings bigger than Crossrail.