According to our DOM any tip over 100 pounds from one person has to be reported to your manager. It's highly unlikely you would ever receive that much from one person and half that an extremely rare occurrence. So that's from the horses mouth ! The comment about alcohol percentage on the other hand is best disregarded.
Regarding the question I would say if a reserve is handed or finds a tip/present addressed to 'our postman', 'the postman', or the name of the regular postman I would hand it to the regular postman. To do otherwise in my humble opinion should be considered theft. If the customer appears friendly and and wants you personally to have a tip then you should accept it.
Of course though we live in the real world, and I'm the regular postman, so if the reserve finds a tip on the doorstep I will fully expect them to keep it. Prove me wrong and do the opposite.
The views I express here are mine alone and do not represent the views of Royal Mail Group.
