The FCA issued the warning as it reminded firms that the new MiFID II rules apply from 3 January 2018, and applications for permissions must be completed by 3 July 2017.

In a statement, the regulator said: “Firms who need to change their regulatory permissions as a result of MiFID II should submit a complete application for authorisation or a variation of permission now, to ensure that we can we determine it before MiFID II takes effect.

“We expect firms to be busy considering what impact MiFID II will have on their business and to act accordingly.

“Most applications are not complete when they are submitted. Firms who have not already done so should therefore submit applications as a matter of urgency to help us identify as soon as possible what, if any, further information is needed to complete the application. We cannot guarantee that any application which is only complete after 3 July 2017 will be determined by 3 January 2018.”

The FCA warned: “Firms that carry on MiFiD II activities without the necessary permissions may face civil, regulatory and/or criminal consequences.”

For firms affected by MiFID II, FCA officials said its application and notification user guide can help show the steps companies may need to take. The FCA phone number for this is 0300 500 0597 from the UK, or +44 207 066 1000 from abroad.