Probably London's most expensive tree is a London Plane (Plantanus x acerifloia) in the gardens of St Mary Magdalene Church, Islington.
According to Islington council it has been independently valued at over one million pounds. Its girth is over seven metres and it’s approximately 300 years old. https://twitter.com/IslingtonBC/status/1064477165528539137
Upper branches and canopy not shown.
Photos taken November 2018 with Sony a6000 and processed in Agisoft Photoscan.
https://www.monumentaltrees.com/en/gbr/england/greaterlondon/4523_stmarymagdalenechurchholloway/