here is the euro control link for Raim prediction.
http://augur.ecacnav.com/status.html
The NPA tool is for approaches. And as such can be ignored in the UK.
Another page which may be of interest is
http://www.ecacnav.com/GNSS
It also lists out when all the project should come to pass and what you can expect the end service to be.
And another link from the royal college.
My view is that its a very useful tool in the tool box. It does need backup and a certain amount of training to be provided to inform the user of its limitaions and its failure modes.
As a matter of interest can you get a combined GPS/VPU for light aircraft?