Measure overwhelmingly passed in Mexico state's Congress on April 21
Government conference to coincide with London Pride's 50th anniversary
ITV broke story on Thursday
Country's lawmakers urged to ban discredited practice
John Mason compared practice to treatment for eating too much chocolate
Measure passed by 112-8 vote margin
Lawmakers must codify prohibition
GLAAD praises policy announcement
The National Assembly unanimously approved ban
Handful of countries now prohibit discredited practice