Who actually owns a pillbox that is on their land?
The landowner.
 What was the original legal position when the land was requisitioned?
The land was requisitioned under the war emergencies act (1939 i think)
 Was the land actually ever handed back?
Yes. At the end of the war the land was returned to the owner wherever possible. In some cases the government kept the land if it had a military usage after the war.
 If someone wanted to move a pillbox from one owners land to another, what legal problems would be encountered?
Only the usual ‘problems’ involved in transferring ownership from one person to another. No more difficult (legally) than selling a car or trailer. They are very difficult things to move physically though!
However, before moving the pillbox remember that much of its true importance is it’s location in the landscape. A pillbox guarding a crossroads loses all its significance if it is moved to a garden overlooking a river. It also makes future archaeologists very confused!
 Are pillboxes protected by preservation orders?
Some are, some are not. Check with your county council archaeology department. They will know!