Year Sterling 1997-12-31 13409 1998-12-31 15480 1999-12-31 17777 2000-12-31 17566 2001-12-31 18505 2002-12-31 15201 2003-12-31 13079 2004-12-31 12882 2005-12-31 12912 2006-12-31 12381 2007-12-31 13182 2008-12-31 17027 2009-12-31 14668 2010-12-31 15594 2011-12-31 14134 2012-12-31 14868 2013-12-31 13780 2014-12-31 15263 2015-12-31 18321 2016-12-31 18442 2017-12-31 18875 2018-12-31 21596 2019-12-31 21174 2020-12-31 22553 2021-12-31 21849 2022-12-31 21707 2023-12-31 20764