This grower is fairly sure of this plant identification.
Palm saplings grown from seeds collected from the fruits of 20m+ specimen trees in Andalucia that a friend identified for me as Livistona washingtonia. They are definitely thread palms but I couldn't find much info on the species, it seems obscure. The palms are currently in tall 3L rose pots, so should live happily as container plants without repotting for some time. I have 2 of these available of very similar size.
Livistona genus (Fan palm). This genus has 30 species of evergreen palms, the clusters of flowers are insignificant and will bloom in the summer. The fruits are clusters of blue, black or reddish.
These sub-tropical palms will tolerate frosts down to about 25°F or 4°C. Slow growing, they prefer deep, sandy, well-drained soil. They need good sunlight, but produce more vigorous, deeper green foliage in dappled shade. They make excellent container plants.
Grown for their overall appearance.