Definately recommend looking at the front prop as suggested by rstoughy. I have had terrible vibration for the last 1000 miles or so and in the last week have also been getting a knocking sound which sounded like exhaust banging against something.

Today i jacked the car up to investigate the exhaust problem and noticed the the joint on the front prop is absolutley fooked!

I'll get that replaced soon and hopefully it'll fix the vibration issue.

Good luck mate.