My mechanic swapped the accelerator and break pedals over . . (sorry . . couldn't resist)

 

I don't understand.

 

Have you checked your floor mat is clear of the accelerator pedal?

Sudden Unintended Acceleration (SUA) does seem to appear frequently in the American market (!). Audi (a high profile example, but Toyota has also been stung) has faced lawsuits throughout the 1980's on the issue involving property damage, personal injury and deaths.
Canadian (Investigation of Sudden Acceleration Incidents Dec 1988) and American (An Examination of Sudden Acceleration March 1989) studies, universally found unintended acceleration was a result of user error and to a lesser extent, interface design, a Japanese Study (An Investigation on Sudden Starting and/or Acceleration of Vehicles with Automatic Transmissions April 1989), found no mechanical cause of the phenomenon. The NASA study into Toyota SUA found no fault with Toyota systems and that all reports of SUA were caused by “pedal misapplication,” otherwise known as driver error.

 

I did last March. I was attempting to park in a parking spot, I had slowed to stop but the car seem to speed up, jump the curb and finally came to a stop after crushing a large planter. I thought my foot slipped off the brake pedal but I was conscious of attempting to stop. My car was totaled as the undercarriage was severely damaged. I was in shock and I still wonder if it was a mechanical issue or operator issue.

 

I've had my F54 Cooper SD auto for nearly 2 years and no problem with SUA. It does seem to be an American thing but that could be down to the American market being mainly auto box while a lot of the rest of the world prefer manual. In a manual even if it was user error (and I'm not saying yours was) then you can dip the clutch and knock it out of gear. I have been caught out at the sudden acceleration when I floor it but that's down to me driving my Transit all week and then jumping in the Mini. The Transit is 'slightly' slower to accelerate