We'd like to share with you the implementation dates of BS 7671:2018.  Here's what we know:

1 July 2018 – the standard is published. So, installations that are designed after this date may comply with and be certified to this new standard or be designed and certified to BS 7671:2008+A3 (for a maximum transitional period of 6 months)

1 January 2019 – the standard comes into full effect. So, installations that are designed after this date should comply fully with BS 7671:2018.