Complex sentence: In 2001 he was invited to become Junior Treasury Counsel, becoming Senior Treasury Counsel between 2007 and 2014, and taking silk (i.e. appointed Queen's Counsel) in 2008.
Split into simpler sentences: In 2001 he was invited to become Junior Treasury Counsel, becoming Senior Treasury Counsel in 2007 and serving in that capacity until 2014. Brown took silk (i.e. appointed Queen's Counsel) in 2008.