Having a tricky time with this.
Initially thought it may be the Oxycarpa form of Narrow-leaved Ash (Caucasian Ash) but very unsure.
Any help greatly appreciated.
It is not F. oxycarpa because that has smooth bark and bright shiny green cuppedleaflets.
It is not F. anguistifolia because the leaflets are not narrow enough.
Have you considered Fraxinus americana?
In my mind's eye I can see you scurrying about the streets of London, interest peeked by one tree after another: first glimpsed in the distance, then scrutinised at progressively closer range until dismissed or deemed interesting. Keep it up!
You literally couldn't be more accurate.
My background is in ornithology but have had an entry-level interest in trees since my teens (many years ago now). In recent years however I've wanted to get into them a little more deeply and with the aid of some decent books, and of course the internet these days, have spent alot of time seeking out and endevouring to identify what I can. London is like an enormous arboretum so plenty to look for and study but, even so, the learning curve has been almost vertical!
All brilliant fun though enormously engrossing.
I must say, you've been a great help and it's good to know that if I come across something that baffles me one way or another (all too often) that I can ask for some assistance and will recieve it in a constructive and encouraging way.