1. A method providing means for estimating an indication of integrity of a satellite navigation system, wherein the method includes carrying out the following steps in real time in order to estimate an indication of integrity of the system with respect to location errors of very low probability: measurement of data calculated by the system; calculation of a model of distribution of location calculation errors of the system; determination of parameters (a, b, c) characterizing the distribution model, a being the parameter defining the most probable value of the distribution, b being the parameter indicating the skewness of the extremes, and c being the parameter indicating the weight of the extremes in the distribution; modeling, in the probability domain, of the tail of the distribution by a calculation means as a function of the parameters (a, b, c) applied to the extreme values theory in the following way: H a , b , c ⁡ ( x ) = { ⅇ - ( 1 + a ⁢ x - b c ) - 1 a if ⁢ ⁢ 1 + a ⁢ x - b c > 0 , a ≠ 0 ⅇ - e ⁡ ( - x - b c ) if ⁢ ⁢ a = 0 ; comparison in real time of the distribution of location errors with a tolerance threshold for providing an indication of integrity; and transmission in real time of the indication of integrity of the system.