They're pretty common. More like one every month or three and it's only the big ones that make the news. From a 2015 BBC piece[0]: "A guide on dealing with une

They're pretty common. More like one every month or three and it's only the big ones that make the news. From a 2015 BBC piece[0]: "A guide on dealing with unexploded devices was released by the Construction Industry Research and Information Association (CIRIA) in 2009." "An estimated 15,000 items, ranging from unexploded bombs to small mortar rounds and grenades, were removed from UK construction sites between 2006 and 2008, the association said" [0] http://www.bbc.co.uk/news/uk-england-33861431 http://www.bbc.co.uk/news/uk-england-33861431