Gluten provides 'elasticity' to baked products. Simply replacing an ingredient containing gluten with one that doesn't will result in a sponge that has a different (and probably inferior) texture to what you normally achieve. You need to adjust the other ingredients accordingly, so you should seek out a proper 'gluten free' recipe. This one has excellent reviews:
cake.aspx" title="Link to allrecipes.co.uk provided by user" target="_blank" rel="nofollow">http://
allrecipes.co.uk/recipe/22768/wheat-gluten-free-victoria-sponge-cake.aspx
or, for ease of finding the ingredients, you could try Tesco's one:
cake.html" title="Link to realfood.tesco.com provided by user" target="_blank" rel="nofollow">http://realfood.tesco.com/recipes/gluten-free-victoria-sponge-cake.html