"But where are they going to get this from? I have an NPPL and nobody asks me anything, I don't even have to inform the CAA if I've renewed my medical, how many hours I've flown, nothing!" (Sorry, can't fathom the quote function on PPrune)
The NPPL does not require renewal but its validity is linked to, inter alia, having a current medical which you are responsible for.
Granted the exposure data (i.e. hours flown by NPPL holders) is not collected, nevertheless the CAA has the data on all reportable accidents and the type of licence held.
Those accidents resulting from (possible) medical incapacitation are known and for the NPPL it is one unproven case in the period 2002 to 2008. The NPPL started in 2002. There have been no fatal accidents due to medical incapacitation of NPPL holders from 2002 to 2008.
During the same period there were 8 cases (including one unproven) with PPL(A) holders and two student cases. In the majority of cases the medical contribution was uncertain, and of the 3 PPL (A) cases with a definite or probable medical cause, 2 were alcohol related.
There were approx 22,000 holders of a UK PPL(A) in 2010; since 2002 over 5,000 NPPL licences have been issued, but the stock of current holders is not known as the licence is not subject to renewal.
The risk assessment took this data into account when arguing for the LAPL medical standards.