Certificate

-Universal, there is nothing unsuitable for children. Films under this category should not upset children over 4.
-Parental guidance, but certain scenes may be unsuitable for children under 8.

-Ages 12 and over, films under this category are considered to be unsuitable for very young people. Films in this category may include infrequent drugs, infrequent use of strong language, brief nudity, discreet sexual activity, and moderate violence.

-Ages 15 and over, films under this category can contain adult themes, hard drugs, strong words, moderate-strong violence/sex references, and mild non-detailed sex activity.
-Ages 18 and over,  films under this category do not have limitation on the bad language that is used. Hard drugs are generally allowed, and strong violence/sex references along with strong sexual activity is also allowed.

Because my film has mutants in, there would naturally be a lot of 'strong words', also there's a lot of action and horror scenes, it would not be suitable for children. But there's no drugs or sex scenes/references so i think the film would have a certificate of 15.
Recently most horrors are 15 so i think it is appropriate.