Can petrol be used for cooking in place of LPG?

Not exactly, propane {LPG} uses an open flame for cooking, same as Natural Gas or wood fires or butane stoves.

To use petrol, {oil, or natural gasoline, or even bitumen tar} special stoves are used that do not expose the food to the fumes from the flame. Much like a wood stove, coal stove or pellet stove, these stoves are sealed and you cook atop a cast iron or soapstone stovetop much like you would an electric stove.

** natural gasoline a.k.a. white gas or Coleman stove fuel, is highly volatile and not recommended for indoor use. "Coleman" stoves using white gas, are specifically designed for the use of a pot which separates the fumes from the food. These stoves are expressly designed for camping and have been generally replaced with propane stoves.

***Sterno fuel is jellied "natural gas" or more correctly methyl alcohol (poisonous), some similar fuels use ethanol as well. It is not petrol.