On a quick surf, I think the plant you have mentioned John - Cytisus scoparius - was growing in my garden in my Dads time and there were a few growing when we moved here.
One came up in an unexpected place, and I pruned it into a rounded shape and removed lowers side branches to make it look like a large standard. It was spectacular
Sadly it died, so perhaps it didn't like that treatment
Seedlings used to appear in one particular area, and I pulled them out. I haven't seen any seedlings for years, and now you've mentioned it, I'd like to grow one again.
As I recall, they had a long tap root, so didn't take easily to being potted up after being uprooted. I may not have cared for it properly - it was one of those plants I pot up and don't worry too much if they don't make it.
Ive seen a much smaller variety in gardens around here with very pale cream flowers - a real beauty with arching stems growing to about 4ft. Not sure of its name. Anyone grow anything like that?