The very first thing to establish is whether what you are building actually is a conservatory.
There is no definition in the Regulations of exactly what constitutes a conservatory. This can make it hard to judge whether what is built will be be regarded by your Local Authority as a conservatory or an extension.
This is crucial as as extension usually requires planning consent and is subject to greater building regulation requirements, while a conservatory usually does not require planning consent and the building regulation requirements are much more relaxed.
Conveyancers are good at asking questions about the planning and building regulation consent history behind conservatories forming part of properties being purchased, but less attentive to analysing and applying the answers received.
Below are some general questions ( with guidance on how to treat the answers) which may help. They are not definitive and you should always when considering these matters have reference to the Planning Portal.
Was planning permission required?
Is there a wall within the existing external dwelling which exists between the dwelling and the newly constructed conservatory? If there is not then the general rule is that the work will be viewed as an extension and planning permission would be required.
Was building regulation approval required?
Is it built at ground level? If not and is more than a single storey in height then building regulation approval would be required.
Does it have a floor area of less than 30 square meters i.e. the same as a parking space for a car? If it is more, then building regulation would be required.
Does the glazing comply with Part N of the building regulations? If not then building re building regulation would be required.
Does the electrical work have its own ring main, or is extended from an existing room classed as a special location, such as a kitchen? If so it must comply with Part P of the Building Regulations, which deals with electrical safety. If not then building regulation approval would be required.
Does it have an independent heating system with separate temperature and on/off controls? If not then building regulations would be required.
Is there a new opening within the existing dwelling which creates access into the new conservatory if so then this will require building regulation approval?
It is important to note that even if building regulation approval is not required for the conservatory construction the glazing and the electrical work would still need separate consents.
Keep also in mind that if you are acting for a purchaser and have concerns about consents it is important to check the detailed requirements which you can find on the Planning Portal: http://www.planningportal.gov.uk/permission/commonprojects/conservatories/
Care must be taken because if a problem subsequently emerges then enforcement action can be taken by the Local Authority, which could result in the demolition of the extension.