Ding to Betelgeuse !
The Radcot bridge has had a battle named after it, and also has earthworks from the time of Stephen and Matilda, as well as during the Civil War.
One of them has a battle named after it - and 2 historically separate sets of defenses/earthworks - some of which were investigated on Time Team.
The other one has a name opposite to that in the original question.
I asked for 2 rather than the oldest because there's some dispute about which has priority.
IIRC it was in Enfield and I am sure there used to be a cache celebrating the event :unsure:
I had a memory that it was somewhere in NW London - for Barclays I think - it's amazing what sticks in your mind.