Thanks, Robert / Ethel for the suggestion of the SPADE anchor - I'd not heard of this make before, but looking on the interweb they seem well regarded by those who have used them.
In the event I bought a Fortress anchor - light and, like the Spade, easy to dismantle for stowage. But this season we have been pleasantly surprised by how well the Delta 10kg has held, and as it's a good fit on the bows roller, this will probably remain our bower anchor, with the Fortress as a backup in case of a blow. I might be tempted however to buy a Spade as a third anchor anyways: we've always been overanchored on our past boats!