Hi Geoff,
By all means wait for it to flower but this looks exactly like spring growth on ash to me. It appears to have opposite leaves, Melia is supposed to be alternate and bi - tri-pinnate.
Leaflets seem a bit broad for Fraxinus excelsior could be any of the other three common species (ornus, velutina, pennsylvanica). In parts of the South Island ash are every bit as weedy as sycamore.