Do you know where you will be leaving? You better go back to 2nd grade and relearn your compass rose.
London postcodes always start with:
E/EC - East Central
W/WC - West Central
London postcodes basically tell you almost exactly where you need to be and for the real Londoners (such as the one who lives in this household) you can tell what type of person they are depending on which postcode they live in. Of course this is only a theory nowadays with the amount of foreigners in the city.
It goes like this: E1/W1/NW1/N1/SE1/SW1/WC/EC are the utmost central postcodes.
The range goes from 1-(about) 28. Besides a few exceptions, the lower the numbers, the more central you are, the higher the numbers, the farthest out you are.
Once you get used to it, it's quite simple, because just by the first part of the postcode you know where you should be heading.
This is pretty much the 1st part of London postcodes explained.
What about those other 3 digits??
The second part of it shows the sector (number) and unit (letters) where the address is located. A number (1-0) is always first, then 2 letters, for a group of houses.
London is about 2 centuries old and it's still ever growing... it never stops! Due to its constant development postcodes are always changing or being split, so no one can give a set form, but there are lots of information out there with maps, and information.
Have a look!