Good question as far as I know you can only enter for the cpl written with a valid ppl,this ppl can only be had after one must have passed the ppl written administered by the flight schools.Are you alleging your school allows these westafricans get the ppl without passing the exams?If you have facts to prove this please inform the CAA so your school can be sanctioned for this.As for the caa i think its about time it starts changing comm questions regularly to prevent fraud.