The Norths Align

"As expert map readers will know, when you’re out and about navigating with a compass, there is a difference between magnetic north (where the compass points) and grid north (the vertical blue grid lines shown on OS maps).

The difference between magnetic north and grid north is often referred to as ‘grid magnetic angle’ and it not only varies from place to place, but changes with time. This needs to be taken into account when navigating with a map and compass.

In 2014, for the first time in Great Britain since the 1660s, magnetic north moved from being to the west of grid north to the east. The change started in the very south-west corner of Britain and will slowly progress across the whole country over the next 12 to 13 years. Ordnance Survey wrote a blog on the progress of alignment between magnetic and grid north in Britain back in 2019, which you can read here:

https://www.ordnancesurvey.co.uk/newsroom/blog/magnetic-north-continues-its-march-to-the-east

Now, there is a third line about to come into alignment – true north. This is the direction of lines of longitude that all converge at the north pole.

The triple alignment makes landfall at Langton Matravers, just west of Swanage, in November and will arrive in Poole by Christmas." Source: Ordnance Survey

Read more at: https://www.ordnancesurvey.co.uk/newsroom/blog/magnetic-true-grid-north-align-over-great-britain?fbclid=IwAR35Zekr-NXZQTg1-E_VUkZ1adtTErUn_CtVllJfS8IG6PnhKNGR2fvNN_o

Further reading:

https://www.ordnancesurvey.co.uk/documents/resources/guide-coordinate-systems-great-britain.pdf

http://britgeopeople.blogspot.com/2019/08/when-zero-meets-zero-by-ciaran-beggan.html

https://geomag.bgs.ac.uk/research/modelling/WorldMagneticModel.html