[Doctor_Fegg]

Postcode centroids have been freely available since 2010. freethepostcode was set up before then (as was npemap, a similar site I was involved with: http://www.npemap.org.uk/FAQ.html#whatIsIt ).

Postcode boundaries, however, are still not available openly.

[arjie]

I wonder how much absolute error there is between the actual boundary and a Voronoi boundary. While I'm sure there's some massive IV postcode for which it wouldn't work, if most postcodes are tiny, then the fact that you're off by under a kilometre isn't so bad for routing.