I've got an 06 plate fabia vrs but when i take it above 70 the steering wheel starts to vibrate. It does this all the way to 90 where it calms down. It only seems to do this when i'm accelerating as when i lift off the throttle it stops vibrating. Any ideas??

Wheel balance or out of balance drive shaft. Sounds daft I know that it will only do it under power, but when you lift off all the torque forces reverse under engine braking, so it can still be a simple wheel balance issue. Also check for lumps of mud/crud on the inside of the alloys.

Yep get the wheels balanced...