Found this answer for my own question.
FPTP rules mean that the immediate result will get paid out on as will the official result, which is announced after the weigh-in and any steward’s enquiries have been taken into account. Should a winner be disqualified in the aftermath of the announcement of the official result then it won’t affect your ability to claim your bet as a winner.
There are some exceptions to this. If the horse takes the wrong course, for example, carries the wrong weight or the jockey fails to weigh-in altogether. Also, if a horse is called the winner in error then you won’t get paid on that, either.