Query about how Tax works with lodgers: UK?

I am aware that you are able to have �4250 in rent from lodgers in your own home, with certain caveats. What I don't feel clear on is how it works if you charge rent, such as �200 a month, and then you split bills on top. Are the bill splits still cled as income and therefore are taxable (or not, in the confines of the �4250). I looked all over for the answer to this, and can't find one. Can anyone help please?