Fairly sure the OS national grid (not to be confused with the pylons one) assumes that the British Isles are flat, so Mercator's off the hook for this one.
Elephants and turtles left as an exercise for the reader...
Makes sense.
I've ridden that road half-a-dozen times and after mature reflection I've decided it's slightly uphill heading east.
Probably one of the smallest gradients most of us would come across, but it's steep enough to make it difficult to get any sort of momentum.
Doing it into a headwind, which I did once, turns it into quite a challenge.
That was the time I picked up several audaxers who used me on my ebike as shelter for a few miles.
One of them even called out 'thank you' when I peeled off towards the bridge at Scunthorpe.