By Guy Taylor Two of Britain’s biggest transport operators are charting very different paths on London’s FTSE 250 index. The stark contrast between Firstgroup and Mobico, formerly National Express, was laid bare in the two group’s most recent trading updates. Firstgroup hiked its already bumped-up annual profit forecast, while Mobico shares cratered after it was forced to delay its full-year results, due to audit issues affecting its German rail business. Investors will fear it is becoming something of a pattern. Back in October, a Mobico profit warning fell just a day after Firstgroup initial…