City executives are returning to their desks after the summer break without their usual high levels of optimism this September amid fears that political uncertainty, economic risks and regulatory changes could hamper dealflow until the end of the year.

Jean-Marc Mercier, co-head of global debt capital markets at HSBC, Europe’s top bond bookrunner so far this year, said the European Central Bank's meeting this week and German elections later in the month, as well as worries about North Korea, discussions about the United States' budget and currency moves, meant he was "constructive" but with "a note of caution".