i have just brought a renault grand scenic and ideally need to fit 3 high back boosters accross the middle row of seats, the middle seat isnt quite full size so does anyone know any narrow high back boosters that might fit? i currently have graco ones but they are too wide!

I was just going to suggest Graco as that was the narrowest one I could get. I think you might need to do a trip to a shop to try them out.

Try http://www.britax.co.uk/car-seats/fit-finder
It's only britax seats but you may find what you are looking for :)