Conservatories MAY need to adhere to building regs and I have a letter from my local council stating I should contact the relevant department to be sure. Also, most councils will require that you ask them if you need planning permission and they will respond telling you if you need to apply in your particular instance.
If it's less than a certain size (30m sq), your property is not already extended, and it can be closed off from the main house, then it is likely that you would not need permission, as it would come under "Permitted Development". With plumbed in heating, larger conservatories, open plan to the house, you may need permission, but your council WILL have to decide.
You are not likely to need it built to building regs if the following conditions are met:
* The conservatory has an area of less than 30 square metres.
* If you have a radiator in the conservatory then it must have a thermostatically control.
* The conservatory can be closed off from the main house by a door or other barrier.
* The conservatory walls should be more than 75% glazed.
* Any glazing in the conservatory must satisfy Approved Document N, that is break safely (either be toughened or laminated) or if it is ordinary glass it must be thick enough.
* The conservatory must have a transparent or translucent roof.
* The conservatory is situated at ground level.
But, to be sure the council don't come and knock it down, and you're not on the next edition of the local evening news, check with your council.