Argh! Thought I'd used self raising flour but used plain instead - how can I rescue my cakes?

[Holymoly321]

Am making fairy cakes and have used the last of the butter and eggs. I have mixed in plain flour instead of self raising (!!!) by mistake - is there anything I can do to rescue the cakes? Can I put some baking powder in or something?

yup baking powder is what is in Plain flour to turn it into SR flour. Not sure how much to add though