UK Metal Detecting Permit "was an Error"

[Pipeline News] A group of artefact hunters called the "Troops Detecting Club UK" (354 members) has obtained a seach-and-take agreement to hold a commercial artefact hunting rally on the site of a former 1930s air base in South Cerney, Gloucestershire (the Duke of Gloucester Barracks). The UK Ministry of Defence was taken by surprise on learning the news and confirmed that its policy has not changed and that metal detecting is not permitted on Ministry of Defence land except in highly controlled circumstances. The Ministry of Defence aditted: "this event was permitted in error and has now been cancelled". The UK's Ministry of Defence made an error?