Congratulations on the pass and thanks for the kind comments.
On the job application front, I believe the best way is to go in person and knock on the door. You cannot be ignored so easily and it is a proven method. But, if you want to use letters, you are correct in obtaining the person’s name. Where a name isn’t available, I would send two letters - one addressed to the Transport Manager and another to the HR Manager. Otherwise it’s pot luck. But if it’s an operator with, say, less than 40 vehicles, I would address the letter to “The Directors”. If you want to do some homework you can get their names from the Companies House website.
All the best with it, Pete 