Is it?

...a black poplar?

In fact, two... and another one by the river. They may well be.

I remember someone telling me that they knew of black poplars in Northampton and said they were on the way from the rugby ground to the centre and that fits this location.

The bark is wonderful!

Funny that I had looked for them for so long and, though often passed them in the car, had never spotted them.

Not far away, in another "green space", a labyrinth.

I rather wish I had followed that winding path now... it might have been a meditative experience.