The pressure on investment banks became markedly more severe today after the Office of Fair Trading announced an investigation into their activities.
The OFT inquiry will focus on fees charged for underwriting equity.
Major City institutions, including Citigroup, Goldman Sachs and Morgan Stanley, could find themselves in the spotlight.
It comes as the sector faces intense political pressure as lawmakers investigate avenues for reform in the wake of the financial crisis.
Next week, chancellor George Osborne will launch an investigation into whether the investment and high street retail function of banks should be separated.
Originally a Lib Dem policy, Vince Cable was expected to map out the plan, but it appears the Treasury has taken the project over from Dr Cable's Department for Business.