Jailed drug mule Cassie Sainsbury will marry her fiancé Scott Broadbridge in jail in a 2018 ceremony that the couple's celebrity agent said would be "lavish" and "great exposure".

Sainsbury, 22, is serving a six-year sentence in Colombia's El Buen Pastor prison for trying to smuggle 5.8 kilograms of cocaine out of Bogota airport hidden in packages of headphones.

Broadbridge, who was not with Sainsbury in Colombia, was engaged to her when she was caught. He had maintained that he would stand by her "no matter how long it takes".

Sainsbury was recently granted permission to hold her nuptials behind bars and the traditional ceremony is expected to take place in the middle of next year.