True north and grid north have always coincided, that's not special, that's how the National Grid was set up. But thanks to the curvature of the earth they only coincide perfectly along a single line of longitude, namely 2°W, a line which runs up the centre of the country from Swanage to Aberdeen. Live to the west of this line and grid north is a bit to the west of true north. Live to the east of this line and grid north is a bit to the east of true north. Only if you live precisely on the 2°W line, say in West Bromwich, Hebden Bridge or Berwick-upon-Tweed, might the Ordnance Survey's amazing claim apply to you.
If you've ever done any serious mapreading you'll know that compasses point not to the North Pole but to the North Magnetic Pole, which is somewhere else entirely. On maps of my childhood the North Magnetic Pole was always shown to be in the icy wastes of Northern Canada, somewhere in the vicinity of Ellesmere Island. But it's been moving north since then, more recently at a rate of approximately 35 miles per year, and now sits considerably closer to the North Pole. More importantly it's just on the far side of the pole compared to the UK, close to the 180° line of longitude, so at present our compasses are pointing near enough due north.
If you check the edge of an Ordnance Survey map you'll find a graphic designed to help users with compasses to make adjustments. This is the orientation advice on a map of London published 50 years ago when magnetic north was about 9 degrees west of Grid North. It's a lot closer to 0 degrees today.
The difference between true north and magnetic north is called magnetic variation, or 'declination'. This function varies with time as the Earth's magnetic field shifts, in the short-term predictably and in the long-term not. Here's a snapshot from a NOAA map of the world showing declination as it currently stands, and with a slider so you can track back over the centuries and see how it's changed.
The red lines show where magnetic north is east of true north (including London), the blue lines show where magnetic north is west of true north (including Ireland) and the thicker green line is where the two precisely coincide. The green line is officially called the agonic and has been moving across Great Britain since 2017 when it first clipped the coasts of Kent and East Anglia. It reached Greenwich in the summerof 2019, meaning compasses at the observatory briefly pointed due north. And what's just happened is that the green line has finally crossed the 2°W line of longitude over land for the first time. Magnetic north meets true north meets grid north, just outside the Dorset village of Langton Matravers.
As the green line moves across the country over the next few years the point of triple intersection will move slowly north. It's due to hit Poole at Christmas, Hebden Bridge in August 2024, Berwick-Upon-Tweed in August 2025 and Fraserburgh in July 2026. For a magic moment the Ordnance Survey map graphic will have all three arrows in the same place, and then inexorably magnetic north will edge east of true north for the first time.
But not quite "for the first time in history". Magnetic north has always moved around the planet, and the green line last crossed the British Isles in the 1660s. What is true is that the National Grid hadn't been invented at the time, so technically yes, the 2020s are the first time magnetic north, true north and the UK's grid north have aligned.
Of more long term importance than this triple technicality is the switch of magnetic north from 'a bit west' to 'a bit east'. Prior to 2017 it was always the case in Great Britain that magnetic north was a bit west of true north. Currently it's either west or east depending on where you live and by the end of the decade it'll always be a bit east. Confusingly grid north is going in the opposite direction, from 'a bit east' to 'a bit west'. This change started in Cornwall in 2014, reached Cardiff and Glasgow in 2020, hits Leeds and Newcastle in 2025 and won't reach London until spring 2028.
London norths from west to east before 2019: Magnetic north, True north, Grid north 2019 - 2028: True north, Magnetic north, Grid north after 2028: True north, Grid north, Magnetic north
In summary, ten years ago in the UK it was always the case that magnetic north was west of true north and grid north. In ten years time magnetic north will always be east of true north and grid north, at least until some unpredictable future date when the Earth's magnetic field deigns to nudge things back. And for the time being these things are in flux, with complete equivalence currently only for a small patch of the Dorset coast.
One day there'll be a time when your compass tells the truth. If you're in Swanage that's now, if you're in Wales you have a few years to wait and if you're in London sorry, you've missed it.
