chocolate orange cake/using milk choc?

Hi,

I've been asked to make a cake to celebrate the 2nd anniversary of the bike shop i work in. The logo and theme in the shop is mainly orange so i need to use that so I was thinking of fondant icing the cake with orange icing. I thought it would be nice to make a chocolate orange cake but cant find any recipes. I wandered i its possible to make a chocolate cake using milk chocolate because in which case i could use terrys chocolate orange. failing that, could i substitute cocoa powder for chocolate orange drinking chocolate?

yep uk. just occured to me that there is a dark choc terrys chocolate orange..

i need to get the orange in and i wander if it wouldnt taste better using orange choc rather than orange juice or something? much as i would like to properly ice the cake, i dont think it will work on just any cake will it? when i think of that kind of icing, which i only know as fontdant though i believe thats the american term, i think of xmas cake.