The main requirements of US and UK Intergovernmental Agreement came into effect on 1 July 2014.
UK banks were required to extract account balances at 30 June 2014 and undertake checks depending on the value of the account. Higher value accounts (balances over $1m) were reviewed by 30 June 2015 and lower value accounts ($50k - $1m for individuals and $250k - $1m for entities) will need to be reviewed by 30 June 2016.