Citigroup's work on the largest M&A deals announced so far this year has given the bank a lead in the league tables - and has been greeted cautiously by bosses as proof that it is making its mark with transformational transactions.

Citi is advising Essilor, a French manufacturer of lenses for glasses, on its merger with Luxottica, an Italian company that makes glasses frames. The deal is valued by Dealogic at €24 billion. The bank is also acting for US healthcare group Johnson & Johnson on its $30 billion acquisition of Switzerland’s Actelion.