Q.Eucalyptus Tree
I have bought a house and in the garden is what I think is a eucalyptus tree with ovoid leaves 2-3 inches long. The tree is 10 feet high and only has leaves on the top two feet. Lower branches may be dead. It has been planted in a small pot where it has had to struggle for light.
If I plant it out in a sunny spot, should I cut it back first?

Having no idea what your winter temperatures would be, I don't know if it would be winter hardy in your area. IF it is, I would plant in the ground, and give it time to get somewhat established before drastic pruning. If the plant isn't going to be winter hardy, transplant into a larger container and slowly prune to attain a smaller plant that is the shape you prefer.