Any internal decorating such as wallpapering, new skirting boards or painting will not normally require approval under the Building Regulations. There are, however, other considerations to bear in mind and work on external walls is treated differently.
External walls are considered to be thermal elements (defined in Regulation 2a of the Building Regulations 2000 (as amended)). It is likely that a renovation of a thermal element could trigger a requirement to upgrade the thermal insulation of that element at the same time.
The scope of the Housing Act 2004 means that requirements over internal finishes could be made under it. However, in practice, the Act is not likely to be used in this way for work within the confines of normal domestic premises unless the new covering poses a particularly serious risk - for example in terms of fire spread. The local authority will be able to advise on the application of the Housing Act in practice. Further information about the Act and the Housing Health and Safety Rating System which supports it is available on GOV.UK.