Thanks for getting in touch.
The vibration is felt through the seat and a little through the steering wheel. It's generally worse around 55 moh and the frequency increases with speed. This gives the sense that it improves with speed!
I wnt this morning to have the tyre pressures checked as I had fitted new tyres. I found they were all set at 2.2 bar, I've had the rears set at 2.5 and this seems to have had a positive effect although the vibes are still there.
Next week I am visiting a garage with a rolling road so I can identify where the problem lies and visually check whilst running the car.
I will report my findings