Most conservatories can be erected without formal planning permission under Permitted Development rules. Go to https://interactive.planningportal.co.uk. Click on the type of property and you will see an interactive picture which you can explore.
Because of inherent heat losses in a conservatory, the conservatory has to have separation from the main property, e.g. by French doors or patio door.
A Conservatory has to have at least 76% glazed roof otherwise it is regarded as an extension in planning terms. A conservatory has to have heating independent of the main house, e.g. plug in electric heaters but not radiators linked to the main house central heating system.
Larger conservatories may require to comply with the Neighbour Consultation Scheme, which means if a neighbour objects, the Applicant may have to submit a full Application.