As above forum wise, although I would hazard a guess at the throttle position sensor or the pedal position sensor all cheap items (at least on other cars never owned a BMW mini).
The car is telling you what's wrong though so I wouldn't go part throwing and waste your money. Take it to a garage, dealer or friend and get them to read the fault code off the system. Some cars even have a system built in to show the fault code without a reader but other forums would know more about this.
Once you have the fault code then target the problem, it's always cheaper to know rather than guess in the long run.
Edited by Hewlett_T, 17 August 2017 - 06:50 PM.