We’ve got one, kindly supplied by Admin. The two local authority wards (Marple North and Marple South) are a legal definition.
This is going to sound really pedantic, but...
They are a legal definition of two electoral wards. That's all. When push comes to shove, all an electoral ward is is an area of land used for electoral and democratic purposes. They don't necessarily line up with anything. I used to live in the London of Borough of Merton, in the ward of "Lavender Fields". There's no town or area called Lavender Fields. It was just a name they gave the ward because otherwise it would have been called "Most of Merton Abbey, Bits of Mitcham, and a few other things".
I'd agree they are a fair basis for defining the "Marple area". But they're not a legal definition of the town of Marple - if for no other reason than that the wards include the villages of Compstall, Mellor, Strines and High Lane. Oh and Marple Bridge if you assume that's a distinct entity from Marple.