It can’t!
But…your insurer may be able to. If for example you are paid to use your car to deliver food in the evening or at weekends, but you choose not to disclose this fact to your insurance company, then any claim you submit will be closely scrutinised. The claims handler will ask what the car was being used for at the time of the accident, and will look to corroborate the answer you give with information from other sources.
Honesty is the best policy – tell your insurance company in advance if your circumstances change and you take on additional work which involves using your vehicle as a taxi or to deliver goods. Your premium will go up, but you’ll have the peace of mind that you’re driving legally and you’re properly insured!