Check this mini guide out Xenon - although sounds like it's too late anyway
It says that for the conservatory to not need planning permission it must be 3M or less in length - yours is 4M right, like mine?
For it not to need Building regs it needs to comply with the following:
1.They are built at ground level and are less than 30 square metres in floor area.
2.The conservatory is separated from the house by external quality walls, doors or windows.
3.There should be an independent heating system with separate temperature and on/off controls.
4.Glazing and any fixed electrical installations comply with the applicable building regulations requirements (see below).
You are advised not to construct conservatories where they will restrict ladder access to windows serving rooms in roof or loft conversions, particularly if any of the windows are intended to help escape or rescue if there is a fire.
Any new structural opening between the conservatory and the existing house will require building regulations approval, even if the conservatory itself is an exempt structure.