Plain Flour

This is what Nigella says:

Just add 2 teaspoons of baking powder for each 150g/6oz/1 cup plain flour. Sift the flour and baking powder together into a bowl before using, to make sure the baking powder is thoroughly distributed.

I meant to add the link:

www.nigella.com/ask/self-raising-flour

In the olden days my little pots of baking powder would have a list on the side showing how much to add to plain flour depending upon what you were making. So it was something like 3 tsp per 8 oz flour for suet pudding, sponge cakes and scones, and 1-2 tsp for a rich fruit cake or biscuits if I remember rightly.
Having said that, though, I reckon Nigella's 2 tsp per 6 oz to cover everything is a much easier ratio to remember!

Thankyou xx

Yes it’s easy enough to just add baking powder, be careful not to add to much though, it can leave an after taste.

Thank you the cakes turned out fine.