In most circumstances you will not need planning permission for a new conservatory, which obviously makes the whole process a lot easier. As always with these things there are exceptional circumstances where by permission should be sought. If in doubt you should contact your local authority for confirmation. This especially applies in Scotland where the rules differ somewhat from the rest of the UK.
There are several things to consider when deciding if planning permission is needed. The size of the structure has a bearing and whether the property is a terraced, semi-detatched or detatched house. Also, the size of the garden is important as the conservatory cannot occupy more than a certain percentage. When your designing the conservatory take into account the position relative to property boundaries. If the conservatory is to be used as a commercial entity than permission is normally needed or if the conservatory is to be used as a seperate dwelling.
The type of conservatory, whether timber, aluminium or uPVC does not normally impact permission. Neither does the style, for example victorian, georgian or lean-to conservatories. It is the size and position that matter must.
If you are building the conservatory yourself then definitely check the local building regulations and planning department to make sure your are not infringing any rules. If the conservatory is being built for you, then your retailer should guide you in the right direction.
Always check with your local authority as it worse thing that can happen once you've built your conservatory is that you have to take it down.