If a house has been altered in any way since its original construction, that work would require either a certificate of planning compliance or a certificate of exemption. Usually, the person employed to do the construction work would provide such a certificate though an engineer, Building Surveyor or Architect.
Identifying Changes to the Property
When you go sale agreed and hire a surveyor, during the survey, the surveyor will attempt to identify any changes to the property and give their opinion on whether or not that change needs a certificate of compliance with planning or a certificate of exemption.
For example, if there is a rear extension to a property that is under 40sq meters, that extension would not need planning permission and so an architect, engineer, or Building Surveyor would need to produce a document confirming that in their opinion, the extension is exempt from planning permission.
It is the responsibility of the vendor to produce these certificates for their solicitor. That solicitor will then share it with the buyer's solicitor to ensure everything is in order.
Who Provides the Certificates
In some cases, vendors have these documents ready to share and everything can go smoothly. In other cases, the vendor may not have ever received one or may not even be aware they needed one. In this case, the vendor should engage a professional to provide their opinion on compliance or exemption.
This is all so your solicitor can make sure that you will not face any legal risks with regard to the property itself and its adherence to planning laws.
What to do if the Buyer cannot or will not produce a cert?
Of course, no two home-buying journeys are the same, and there may be a case where as a buyer it may be simply quicker or easier to get a certificate/opinion on compliance or exemption yourself. Especially if dealing with difficult vendors. If that is the case, in our opinion, it should not be completed by the surveyor who conducted your pre-purchase survey. As they gave their opinion on a planning/exemption requirement, it would then be a conflict of interest for them to charge you for that service also.
Planning regulations, planning permission, compliance, and exemption can be very complicated subjects. If you are ever in doubt, ask your solicitor to explain the requirements and risks. They may seek the opinion of the surveyor while the surveyor is on-site before offering legal advice on the matter.