Thankyou to everyone for taking the time to reply, sorry it's taken me so long to get back to you. I haven't been able to come to a decision so have literally bought us a little more time. I'm reconsidering donating but am going to do a bit of research around children who have been donor conceived. I found a website called The Donor Conception network ( I think) and it looks quite good.
What a thoroughly modern dilemma!
Xx
Numa