I had a similar problem with a similar cause last October.
I was able to get it repaired under my insurance, only paying the £75 excess.
Customer service at RS provided technical details I could share with the professional repairer. I used Bryan Willis Marine in Larne (NI) and he was very good.
He cut two holes into the deck and conducted the repair to the front of the daggerboard slot through those. While he was there he noticed another crack between the daggerboard slot and bottom of hull which he also fixed.
While I'll happily tackle a few repairs myself e.g. the mast ring retrofit/upgrade, in hindsight I am really glad I left that one to the professional.