Mail is slightly different. It isn’t a natural monopoly because the roads that the deliveries run over are publicly owned and maintained so the cost of starting a new delivery company is low. Switzerland has the same model for Internet and apparently it works very well: three fibres go from your house to the exchange, but companies can compete to provide you with the service that runs over them.
The problem with privatising delivery is that we learned a long time ago that completely disconnecting people from the postal service causes huge problems and so you need at least one delivery operator with a universal service guarantee. And that has to come with some price control that makes delivering to some people unprofitable.
If the price setting is centrally controlled, there isn’t much scope for competition. There are a lot of economies of scale and the largest player will win. This will tend towards monopoly.
If the new players are exempt from the universal service obligations then they will focus exclusively on the profitable areas. This takes away business from the operator that has to cover all addresses. This makes them start to lose money. If they are privatised, they will go bankrupt and need bailing out. If they are public, they will become a revenue sink, indirectly subsidising the profitable companies.
I would love to see last-mile delivery taken back into public ownership. We often get half a dozen or more delivery vehicles on our road in a day, damaging the road. We’ve had a single order from one company shipped via three different couriers and end up arriving on the same day, spread out over a few hours. Requiring the Royal Mail to accept next-day and same-day (if arriving sufficiently early) parcels at all of their distribution centres and giving them back their delivery monopoly would improve efficiency enormously.
@david_chisnall @12thRITS @anon_opin An Open University tutor told a memorable anecdote about externality.
He worked for Royal Mail and saw that private couriers would take the easy profitable business (like deliveries in cities) but put expensive deliveries in the public postbox and let Royal take the hit (to remote addresses like the Outer Hebrides, for example).