Acacia dealbata? crocus sell it plus any of the nurseries listed at the bottom of this page. Their webpages also have cultivation advice. They are not very hardy but you should succeed in Kent.

Thank you! It's actually not the dealbata which has ferny leaves - it has willowy leaves. It may be the retinodes, but I am not sure. There are so many kinds... But thank you so much for replying.