if you are concerned that you have heavy clay soil,do not pay £65 per tonne for somthing you do not need ,because magnolia love heavy clay, just make shore it has good dranige.

Magnolias prefer leafy slightly peaty material for their roots which are soft and fleshy. Sticky clay would not allow the top growth to be adequately supplied. They can look good for a few years but if the roots are damaged or in clay, they will succumb. They are trees for the edge of woodland. I am sure your Norfolk soil would be fine for it.

Heather, I am sorry that I have to disagree, magnolias prefer just like a number of plants' clay, there are a lot more nuterents in clay than the soil you recomend, and I fail to understand why clay would damage root systems, it would be more lickly to protect them, they also need a slight acid soil which is in clay. I have nothing aginst interducing lome in to the soil as it helps the plant to extract the nuterents,