Planning Permission
Under new regulations that came into effect from 1 October 2008 adding a conservatory to your house is considered to be permitted development, not needing an application for planning permission, subject to the following limits and conditions:
No more than half the area of land around the "original house"* would be covered by additions or other buildings.
No extension forward of the principal elevation or side elevation fronting a highway.
No extension to be higher than the highest part of the roof.
Maximum depth of a single-storey rear extension of three metres for an attached house and four metres for a detached house.
Maximum height of a single-storey rear extension of four metres.
Maximum depth of a rear extension of more than one storey of three metres including ground floor.
Maximum eaves height of an extension within two metres of the boundary of three metres.
Maximum eaves and ridge height of extension no higher than existing house.
Side extensions to be single storey with maximum height of four metres and width no more than half that of the original house.
Roof pitch of extensions higher than one storey to match existing house.
No verandas, balconies or raised platforms.
On designated land* no permitted development for rear extensions of more than one storey; no cladding of the exterior; no side extensions
Planning Permission
Under new regulations that came into effect on 1 October 2008 an extension or addition to your home is considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions:
No more than half the area of land around the "original house"* would be covered by additions or other buildings.
No extension forward of the principal elevation or side elevation fronting a highway.
No extension to be higher than the highest part of the roof.
Maximum depth of a single-storey rear extension of three metres for an attached house and four metres for a detached house.
Maximum height of a single-storey rear extension of four metres.
Maximum depth of a rear extension of more than one storey of three metres including ground floor.
Maximum eaves height of an extension within two metres of the boundary of three metres.
Maximum eaves and ridge height of extension no higher than existing house.
Side extensions to be single storey with maximum height of four metres and width no more than half that of the original house.
Two-storey extensions no closer than seven metres to rear boundary.
Roof pitch of extensions higher than one storey to match existing house.
Materials to be similar in appearance to the existing house.
No verandas, balconies or raised platforms.
Upper-floor, side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor.
On designated land* no permitted development for rear extensions of more than one storey.
On designated land no cladding of the exterior.
On designated land no side extensions.
This is lifted directly from planning portal
I think that buildings regs is required, if certain other requirements are not met ie roof, heating, doors between house and conservatory.