My son has a F1 visa in his UK passport, which is still valid. Due to circumstances, he is unable to continue his studies in the US and has returned home. However, he needs to return to the US for a different reason than his F1 was given. Can he apply for an ESTA with a current F1 visa still in his passport?
If he has discontinued his program of study, then his student status will have been terminated and the F1 visa will no longer be valid for travel, even if it has not been physically stamped with a cancellation stamp.
That is no bar to travel under the Visa Waiver Program. You can continue to use the program, obtain an ESTA, and travel to the United States as a visitor.
But be aware that if he returns to the US as a visitor soon after discontinuing a program of study, the border officer may suspect that he is trying to live in the United States. He should take extra precautions to be able to document the purpose of his visit at the border and his intentions to return to the UK.