The free map is 1:250k, but Bing Maps uses the 1:50k I think (it could be the 1:25k though, it's very detailed and has stuff like footpaths). It certainly looks better than the 1:250k.

Have a look at https://binged.it/2BFM0UA

And compare to the OS 1:25k example image: https://www.ordnancesurvey.co.uk/business-and-government/pro...