Lepton flavour universality and lepton flavour conservation tests at CERN

A precision lepton universality test by measurement of the helicity suppressed ratio of leptonic decay rates of the charged kaon with 10e5 K+- ->e+- nu decays collected by the NA62 experiment in 2007-08 is presented. The record accuracy of 0.4% constrains the parameter space of new physics models with extended Higgs sector, a fourth generation of quarks and leptons or sterile neutrinos. An improved upper limit on the rate of the lepton number violating decay K+- -> mu+- mu+- from the NA48/2 experiment, which probes the resonant enhancement of the rate in the presence of heavy Majorana neutrinos in the 100 MeV range, is also presented.