Conversion of a Bedsit to Self Contained Accommodation

HMO Licensing

I own an HMO,a large victorian property,which lends itself to convert a large bedsit into a self contained unit. All alterations are within the space already occupied, therefore no major structural alteration, and there will be no increase in the number of tenants. The shower/toilet will be constructed with plasterboard,insulated,heated and ventilated. What planning permission if any do I require.
I refer to an article in the July/August issue of RLA Magazine on page 8 regarding case precedent of Winton v Secretary of State and Guildford District Council. Which has the inference of planning not being necessary, please will you clarify.
Thank you
Tony Vale