Post: 12 March 2014
Last updated: 20 February 2016
These are the current best primary sources for bulk address data for GP practices in the UK, as far as I am aware:
England and Wales
GPs, GP Practices, Nurses and Pharmacies (HSCIC)
Format: CSV
Licence: OGL
England only
GPs and GP Practices (NHS Choices)
Format: CSV
Licence: OGL
Wales only
GP Practice Analysis (NHS Wales Shared Services Partnership)
Format: XLS
Licence: unclear
Scotland
Practices and Their Populations (ISD Scotland)
Format: XLS
Licence: unclear; seems to require specific permission
Northern Ireland
GP Practice Lists (NHC Business Services Organisation)
Format: XLS and PDF
Licence: OGL
Photo credit: The Jericho Health Centre, Oxford by Kaihsu Tai, GNU Free Documentation License