Zetec 2008 Clutch issues

[Deb]

Hi, I bought a second hand Ford Fiesta Zetec Climate 2008 last week with only 43,000 miles on the clock. Immaculate inside and out, one previous owner.  

I collected it on Monday and whilst out driving it started revving really badly, very high, smoking and I had to pull over. It seemed to right itself and I thought it was just me and the new car but today while I was on the main road it did it again and went crazy.

Thankfully I managed to get across three lanes and parked on a pavement before it stopped moving entirely. It won't move forward, only revs and smoke accompanies it. It is under warranty but would anybody know what the issue is? Scared the life out of me. 

Thanks in advance.