Seems I have either a knackered cv joint or a worn wheel bearing. I know what to do if it's the bearing but if it's the cv joint, can I replace the cv or is it easier to replace the driveshaft?

CV joint can be fairly easily removed from the driveshaft, so no, you do not need to change them both - but be warned it is a messy horrible job!!

So am i barking up the right tree here? The car is making a whirring noise in a straight line which gets quiter the faster i go but louder the slower i go.It seems to feel like a grinding when i turn either left or right. I can also feel a vibration beneath my feet when im doing 20mph.

That is sounding more like a driveshaft issue.

Thanks mate, ive decided to stop worrying and guessing and booked it into my local indy garage on monday so fingers crossed!

Yea, i'd say shaft as well.