Unexploded bombs and shells which have been buried by their fall do not pose a significant threat.
Bombs and shells which detonate properly produce a hole and shrapnel.
Unexploded unitions (UXBs) are different. These contain a mechanism designed to detonate the high explosive charge after impact. However, after being dropped from 30,000ft, hitting the ground at high velocity and penetrating some 20-30ft into the drift and still not gone off - you can assume that the device was faulty and has not been improved by the impact and 60 years of burial.
As part of a site investigation, all that is normally required is a search at the Public Records Offi ce, Kew, Richmond, Surrey TW9 4DU, tel: (020) 8392 5200 www. pro.gov. uk/ to see if any report of a UXB was made. If there was, then you will have to make further investigations on site.
Normally there is no such record (but remember that no record does not mean there is no UXB on the site).
There has not been one instance of a UXB exploding in England in spite of all the redevelopment that has gone on since the war. It poses an insignificant risk unless you find one. Then call in the Army professionals.
Much can be made of the inherent risk but experience has shown that little exists.
Simon Harbottle (M), 52 Tintagel Way, Oriental Road, Woking, Surrey GU22 7DG