On 15th May 2018 EASA published a report presenting the data and analysis of an investigation they carried out earlier in 2018 to understand the current status of the deployment of ADS-B and other means of surveillance.
From a UK perspective, the map extracted from the report presented below is of particular interest.
The full report can be accessed via the link below.
SESAR Deployment Manager
ADS-B and other means of surveillance implementation status
May 15th, 2018