Thinking about it, I disagree that you will require planning permission. This is just a shed. You could move the stuff piled up in the spare bedroom into it and use the spare bedroom as your 'salon'. You would not require planning permission for that, so I cannot see why you'd need planning permission for a shed - unless it was larger than PD limits.
An outbuilding needs to be incidental to the main use of the house, that's the difference between it being a room in your house, that you may do ancillary operations etc, and an outbuilding (in terms of usage)
Thanks that seems to kind of answer my question, I think what I'll do is phone the council and just state that I intend on using a garden office as a salon and go from there. It would also seem the main cause for concern is access which I don't think will be a problem as my neighbours to which it would effect are fine in fact they would probably support the venture - those that aren't deaf or slightly aged
Even if everyone around it approves of it, doesn't mean it is going to get approval unfortunately. In reality, lets say you had awful neighbours move in, then your proposal should not effect them either (and not give them reasonable grounds to object on planning terms) Depending on the council and the way they work I would still speak to them (nothing formal) and get an opinion from them.
If you did go down the route of applying for planning permission and the buildings already built, just a floor plan would be fine.
If you don't think the neighbours would mind, you could always go ahead and just do it, and apply retrospectively - if no one complains, the council wouldn't necessarily know or be concerned.