  Measured ratios of decay rates for Ke3/K2\pi, K\mu3/K2\pi and K\mu3/Ke3 are
presented. These measurements are based on K^+- decays collected in a dedicated
run in 2003 by the NA48/2 experiment at CERN. The results obtained are
Ke3/K2\pi = 0.2470 +/- 0.0009 (stat) +/- 0.0004 (syst) and K\mu3/K2\pi = 0.1637
+/- 0.0006 (stat) +/- 0.0003 (syst). Using the PDG average for the K^+- ->
\pi^+-\pi^0 normalisation mode, both values are found to be larger than the
current values given by the Particle Data Book and lead to a larger magnitude
of the |V_{us}| CKM element than previously accepted. When combined with the
latest Particle Data Book value of |V_{ud}|, the result is in agreement with
unitarity of the CKM matrix. In addition, a new measured value of K\mu3/Ke3 =
0.663 +/- 0.003(stat) +/- 0.001(syst) is compared to the semi-empirical
predictions based on the latest form factor measurements.
