The government took control of all munitions works during WW1 and most were closed before WW2. During the 1930s, Royal Ordnance Factories (ROF) were built to increase manufacturing capabilities in case of war. The new factories were often sited in north and west of the England to provide some protection from aerial bombing.
The factories often had testing facilities and were sometimes converted into storage areas. Unfortunately, disposal of munitions at these sites was often far below the standards that would now be expected and ordnance was simply buried. An assessment of risk from UXO at these sites should always be completed.
It should be noted that there is also a risk that chemical weapons and their residue could be present at some storage sites, as demonstrated by recent discoveries of mustard gas. Project Cleansweep was an assessment by the MoD of the areas that that may be contaminated by Allied chemical weapons and a summary is in our downloads section.