There are three norths that regular navigators will be familiar with: grid, magnetic and true. Grid north is the direction of a grid line that is parallel to the central meridian on the National Grid – the system of reference on Ordinance Survey maps.
True north is the direction of a meridian of longitude, while magnetic north is the direction a magnetic compass points to. This latter north is affected by changes in the Earth’s magnetic field and therefore shifts very slowly. It now lies east, not west of grid north in parts of south west Britain for the first time in over 220 years of map making.
Ordinance Survey has created custom made maps to help you with navigating, and there’s also a website where you can calculate north on your trips.