Bicycle Tag of bike

new

no proper internet at the moment. Will fill in the details later.
New tag is next to the blue plaque for the person who created the location.

ok, back from birthday dinner with a bit more time.
I see someone already posted the info abbout the location. It's a real london curiosity and a fascinating hidden landmark.
My new tag is also something of an oddity. It has a very misleading name and despite being rather old is still being altered today, albeit several miles from the tag location.
Easing north... initially green fields, crossed by lanes; but wait a bit! More hills! Inch over them and you're there.

This one has really got me stumped. How about another clue?