A quick guide to building a pgRouting network from Ordnance Survey's Meridian2 dataset. It assumes you have a working PostgreSQL/PostGIS database. The most current information will be on Github: https://github.com/mixedbredie/meridian2-for-pgrouting Get the data Download the Meridian2 shapefiles for the UK from https://www.ordnancesurvey.co.
This document and repository explains how to load Ordnance Survey ITN GML into a PostGIS database with Loader and then build a network suitable for use with pgRouting. The network will have one way streets, no entry and no turn restrictions, mandatory turns and grade separations for over- and underpasses.