I can't imagine having a Grapefruit tree in the garden...it wouldn't survive in the conservatory as there is no proper heat in there either...lucky you!!
I wish I could grow citrus here. Oh well. I hope yours produces.
My neighbor here in SoCal grew a grapefruit tree from a seed (before we moved next door). It is now ten feet high with lots and lots of fruit. Oops there goes another grapefruit tree plant!