  The ratio $R_K = \Gamma(K^{\pm}\to e^{\pm}\nu(\gamma)) /
\Gamma(K^{\pm}\to\mu^{\pm}\nu(\gamma))$ provides a powerful probe of the
structure of weak interactions. It is calculated with very high precision
within the Standard Model, but corrections due to the presence of New Physics
could be in a few percent range. Development of NA48/NA62 method based on test
data samples of 2003-04, and the status of analysis based on a dedicated 2007
run are discussed. In addition, a proposal to measure the ultra rare decay
$K^+\to\pi^+\nu\bar\nu$ at the CERN SPS is presented.
