Hi Janey, I so glad you have managed to make a beautiful Victoria Sponge, they are delicious!
For a 4 inch, I would increase the ingredients to 300 grams of butter/margarine, 300 grams sugar & 300 grams of self-raising flour and use six eggs. This will give you enough to make a 4 inch. If you have any batter left over put it into cupcake cases and bake on 180°C for 18-20 mins on the middle shelf.
Hi Janey, it's no bother.
To make the 6 x 3-inch cake you would need to reduce the ingredients to 150 grams butter/margarine, 150 grams sugar, 150 grams self-raising flour and three eggs that should be fine. The same recipe will also make 12