Hardy Tropicals UK

I am just wondering how deep would the roots of this plant go as it matures?

I'm thinking of getting one for someone as a present but their topsoil is only 20 inches deep before you get to gravel which was dumped in when the garden was built. Would this be enough for one of these to grow to a reasonable size?

I have already ordered one for my garden but depth is not an issue for me.

yes.............. the roots go out horizontally in my experience, so nearly 2 foot is plenty