GPS Integrity and Potential Impact on Aviation Safety
The CAA has published a report of a study of "the level of safety as measured by the integrity (i.e. trustworthiness), afforded by the Global Positioning System as a source of navigation data for civil aircraft."
The study presents "a number of augmentation methods which have been shown to have the potential to satisfy the required navigation performance requirements for all phases of flight."
It's a large file (2.9mb) so you may wish to right-click on the link, select
'Save target as...' and save the file to your computer - especially if you're not on broadband.
Link