Quote From chococake:
If you can get into a PhD programme, then I would probably say you would be able to do it. However, I think it really depends on the area too. Some social science PhDs are probably considerably easier than say a PhD in mathematics.
Heeeyyyyyyyyyyyyyyyyyyy - I'm sure if I were a mathematican (sp??) that a maths-PhD would be pimps ;-).
It's all relative I feel but I do agree with chococake that if you are successful with a PhD application then you should be able to complete. That said it can be difficult to get accepted if your marks are not tip-top. Perhaps if you have work experience of your field it will help but if you're relying on what you call your average marks you will have to do a really good proposal just to get it reviewed and considered.