Nice video from OSGB, explaining the concepts:
As Timelord pointed out earlier, on the UK National Grid, True North and Grid North are only coincident at 2° W, because this is the Central Meridian of the projection.
For most of the last 400 years, the North Magnetic Pole has been wandering around the Canadian Arctic, but 30 years ago it started moving fast towards Russia.
PS Having posted a video link, it turns out I can’t see it in my post. This is a common complaint on PPRuNe these days.
A quick way to see the link is to click on the Quote button below, which will allow you to see and copy the video link.