As per the latest code point open from the Ordnance Survey to August 2020. These typically become available every 3-4 months. This time we have 3,201 new postcodes, 2520 deleted ones and 910 restored or renewed. The UK’s poscodes are actually a pretty good addressing system but they are not perfect as these quarterly refinements show.
Each postcode typically covers about 26 addressees only. So you could actually just about post a letter to that one postcode and a name and the Royal Mail would work out which building it should go to with some additional effort. Many other countries have a town number for a postcode which gives you very little granularity. The Republic of Ireland probably has the best system, with one code – an Eircode – for every single address.