Hi Dotty, first of all well done for choosing such a beautiful tree, one of my all time favourite autumn trees, truely magnificent, plenty of raking up mind you!
Purple beech ~
Fagus sylvatica will grow extremely weel in Derby's rich soils, avoid areas constantly wet, marshy ground for instance. It will prefer soil with a pH of 5 - 6.
Without a photo of your particular tree it is hard to give you advice that is relevant to your specific problems, however here is my view on the issues relating to the problem you describe;
Unbalanced pattern of branches-top heavy, unfortunately this is all too common due to poor nursery practices, growing saplings too close together, and not properly managing the young trees from the start. At 7 foot your sapling is still very young so all is not entirely lost. Lack of lower branches on young trees tends to result in poor trunk taper, a lack of normal necessary thickening as you move down the stem towards the ground, and this is very important. Without that taper your sapling is likely to be unable to support itself when in the ground.
Pruning a young beech tree (that is to be grown as a single specimen tree) should not be necessary unless there are very obvious structural problems relating to crossing/touching branches very weak branch unions, diseased or dead branches....all of these problems would normally result in the young tree being culled by the nursery or just not getting bought. You cannot prune a young tree like
F sylvatica with the hope of thickening its growth habit and end up in 50yrs with a large specimen with a strong natural form and structure.
My advice is relation to pruning your sapling is don't, whether your young tree is worth planting and persisting with entirely depends on the extent of the imbalance, and how badly this has impacted on the normal stem taper you would ideally want to see in a tree of this age. (Again a photo would be really helpful).
To be honest it really depends on how much effort you want to commit to the young tree too, you can (if you want to) plant out saplings with poor taper properly supported by two wooden stakes outside the existing root ball/planting hole with supports attached to the stem form each stake enabling the sapling to move but not sway so far over as to bend and distort the growth of the tree. This support may have to remain for a maximum of two years, after that time remove the stakes before they adversely impact on root growth. I have attached a PDF illustrating this.
16819.pdf
Personally I would probably buy a replacement sapling with better form, that has been better looked after by the nursery to begin with, a great many of the problems we have to deal with as Arborists are a result of poor nursery or management practices when the tree was very young.