The answer is keep going.
Its not meant to be cruel, but, carrying out an emergency stop without knowing whats beind poses real danger to the occupants of your vehicle and the ones following. Only do it for a dog or larger animal, oh, and of course people and other road users.
Only do an emergency stop if you have no alternative.
If you do have time to check your mirrors and stop safely then do so.
Read up about it in the Highway code.