Hi, the foliage looks like Robinia but not sure what variety, I used to have Frisia which was yellow foliage, not sure about the yellow flowers though and Frisia was thorny :-)

Does it have thorns? Maybe it's too young to tell. It looks very much like a Honey Locust from my part of the world but I know it's starting to inhabit other parts of the world. They are very pretty with fern-like foliage but are very weak wooded trees. If you (your boss) lives in an area prone to high winds, ice storms, hurricanes, etc. I advise you not to choose this tree for your property. They get gigantic but will come crashing down with any kind of stress -high winds, ice/snow. Mine fell on somebody's car during a hurricane. My neighbor's fell during an ice storm & took out her green house.

Dorset isn't noted for ice storms Bathgate...

What about high winds?

Agree with Daylily, I would go for a variety of Robinia which has more rounded leaves. Gleditisa has longer leaves.

Whether it's Robinia or Honey Locust, they are both prone to the same problems - seed pods everywhere, weak brittle wood, don't do well in draught. They are a thorny business and you will be pulling up little saplings everywhere. Big limbs or the whole trees come crashing down in storms, smashing cars, houses, maybe people.

It looks like a Robinia, to me. The problem is that Robinia has white to pink flowers, and Honey Locust has greenish flowers, and both have bean pods, not lanterns. A tree with yellow flowers and lantern shaped pods would be golden rain tree, or Chinese flame tree--both Koelreuteria species--but this isn't one of them.

I've just seen a plant called Sophora which has yellow flowers, could be a possibility ? Checked again but leaves look smaller.

Maybe Sophora microphylla, though I wouldn't call the pods "lantern shaped".