I have got an interview for a PhD in 2 weeks time. Does anyone know on average how many people are interviewed for 1 PhD position?

Normally they short list to 6 applicants, but it depends on the interest in the project really.

It's a real "how long is a piece of string" question. One of my friends was interviewed, and it turned out she was the only one that was interviewed - they only interviewed her to make sure whe fit the bill. Other times, there'll be 5 or even more that are shortlisted.

Like premonition says, it depends on the interest in the topic, and the quality of the applicants.