Are UK Postal Codes Analogous to US Zip Codes

I used to be part of the giant mail sorting machine. When image recognition fails anywhere in the country the machine takes a photo of the envelope and sends that picture to http://www.urbandictionary.com/define.php?term=MDEC which is full of mainly students. They type in the address and it whizzes back to be sorted. This happens in real time btw. The people operating the machine in Aberdeen (or wherever) have no idea if the machine read it or if a chump in Plymouth listening to podcasts typed it in. The database only has like 4 address lines. Nothing else is used.

Not long before I departed from England, the Royal Mail had brought me, within forty-eight hours of its posting in London, a letter addressed to "Bill Bryson, Writer, Yorkshire Dales," which is a pretty impressive bit of sleuthing. https://www.nytimes.com/books/first/b/bryson-stranger.html

From the machine sorting perspective, the system only cares about house number and post code. That is the bare minimum you need to get it there guaranteed. Royal Mail take a perverse pride in delivering all kinds of badly and optimistically addressed items, but house number and post code is your best bet. Add full address for guaranteed location.

You don't need the postcode all over the box. For correct formatting, go to http://www.royalmail.com/find-a-postcode and start typing the address just with spaces. So for "36 Swan Street Petersfield", you'd get back36 Swan StreetPETERSFIELDGU32 3ADWrite the addressee's name on a line above that, and ENGLAND (all caps, important) on a line below it, and that's all the address that it needs. The days of the enormous UK address are gone. My sister's address in a tiny hamlet in Yorkshire (too small to even have a pub) used to be nine lines, and now it's four.

Yep, what katemonster said. Use the entire postcode and the format matters so include the space.

I have in the past had letters delivered using just House Number + Postcode. I've sent letters with just a description of how to get to the place, because I couldn't remember the address and they've got there too. The UK postal service is pretty good. (Although whether they retain that commitment post-privatisation remains to be seen) IF you type the postcode into https://www.google.com/maps/place/Petersfield+GU31+5RN,+UK/@50.9567989,-0.9321035,15z/data=!3m1!4b1!4m2!3m1!1s0x48744625cb066a6d:0x3487982371c1a38d you can see just how precise the postcode is.

A Zip-5 US postal code refers to a specific geographic area and routes contained within it. This is not fixed, and there are postal codes added and moved to reflect changing populations. Several companies have tied these to loose geographic areas that are closely aligned (though not perfectly to census ZCTAs. Unlike the US, A Canadian postal code is what is called a 'Milk Run' where the first 3 characters define a specific region and area and the last 3 characters define a specific path to follow. I know nothing about UK postal codes.

Thank you both very much!

In principle an address in the UK is uniquely identified by the post code & the house number (or building + apartment number). So yes, it does help things get delivered much more efficiently.