Translate the following English sentence to French:
"When there is one large and 20 small insurers, then the large one may not have more than 10 per cent of the market share for the exemption agreement to be accepted."
Si il y a un grand assureur et 20 petits, le grand assureur ne peut détenir plus de 10 % de parts de marché afin que ce règlement d'exemption soit accepté.