What to use instead of flour for someone who's allergic to wheat

[wartywarthog]

Apologies if this has been asked and answered already, I've searched the archives and not found anything relevant.

I have to bake something for tea (a cake or similar) but it can't have any wheat in it. Is there something I can substitute for normal flour that works just as well?

TIA

You can get wheat free or gluten free flour in Sainsburys or Waitrose

thanks!