It appears to have been discovered by a team including members from the sugar industry.
They were looking for ways to use sucrose as a chemical intermediate. Most synthetic processes involve multiple steps. I have not found what (if any) final product was in mind.
I can find no evidence that any of the participants were engaged in insecticide research.
I can find no evidence that Tate & Lyle, usually characterised as a sugar business, would have been aiming to synthesize an insecticide from sugar.
Researchers at Queen Elizabeth College, University of London, discovered sucralose in 1976, during a collaborative research program with UK sugar producer, Tate & Lyle, PLC.
From a Sucralose information site
Sucralose was discovered in 1989 by scientists from Tate & Lyle, working with researchers Leslie Hough and Shashikant Phadnis at Queen Elizabeth College (now part of King's College London). While researching ways to use sucrose as a chemical intermediate in non-traditional areas, Phadnis was told to test a chlorinated sugar compound. Phadnis thought that Hough asked him to taste it, so he did. He found the compound to be exceptionally sweet.
This article was written with the help of Professor Leslie Hough whose research student Shashikant Phadnis discovered sucralose
Curiously, these substances might still have been waiting to be tested for sweetness had not Shashikant Phadnis, a graduate researcher, misheard a telephone call requesting samples of the chlorinated sugars for testing. As the call came from a large sugar company it is perhaps understandable that Phadnis thought that the company had requested them for tasting and so he tried them himself. The results are available in UK patents 1 543 167 and 1 543 l68.
From New Scientist (allegedly)
Sucralose is manufactured by a proprietary, patented process developed by Tate & Lyle, and uses ordinary granulated sugar, similar to that used in the home, as the starting material.
Sucralose is technically a chlorinated carbohydrate, and it is made by selectively replacing three hydroxyl groups on the sugar molecule with three chlorine atoms. There are multiple locations on the sugar molecule where hydroxyl groups can be replaced. The trick for making sucralose, to get the best taste, highest levels of purity and the best yield, is to ensure that the sugar molecule is chlorinated in very specific locations only.
From Tate & Lyle
Tate & Lyle is a global provider of distinctive, high quality ingredients and solutions to the food, beverage and other industries
Tate & Lyle, a British sugar company, was looking for ways to use sucrose as a chemical intermediate. In collaboration with Prof. Leslie Hough’s laboratory at King’s College in London, halogenated sugars were being synthesized and tested. A foreign graduate student, Shashikant Phadnis, responded to “testing” of a chlorinated sugar as a request for “tasting,” leading to the discovery that many chlorinated sugars are sweet with potencies some hundreds or thousands of times as great as sucrose. (Walters, 2000)
From Sucralose - an overview, Genevieve Frank, Penn State University