LONDON—There’s no free lunch in finance—except when banks are wooing workers back to the office. London’s financial sector, keen to return to a semblance of normality after the worst of the pandemic, is leading the charge to encourage employees back to their old lives, with some companies even offering free food and social events. It seems to be working; London’s transport operator said this week it recorded its busiest day since the pandemic hit in March 2020, as workers filled once-deserted trains into the capital’s twin financial districts of the City and Canary Wharf. Canary Wharf Group, which runs that district, also said it was busier than at any time since last March. Crowds of office staff thronged its plazas, while City workers bustled on London Bridge and lounged by Tower Bridge in the resurgent September sun. “It feels like London offices post the summer-holiday period should be starting to …