I've just found this document which relates to the 'small dwelling' that the council mentioned to the OP. http://www.newforestnpa.gov.uk/__data/assets/pdf_file/0003/96096/extensionstodwellings.pdf
Skim reading it says to me that he wasn't able to extend the bungalow as the total habitable...
Unless I'm missing something I read the 3rd post "I know that permitted development rights do apply in my area, just not sure what the limits are, can i build out 3 mters or 4 meters?" to mean that he HAS Permitted development rights in tact!
As your bungalow is detached you can go out 4 metres from the rear wall.
Check out the planning portal for a visual guide of what you can do under permitted development.
http://www.planningportal.gov.uk/permission/commonprojects/extensions/miniguide
Have you got an existing pitched roof extension by any chance as they use the additional roof volume added there as part of your 50m3 / 40m3 total limit?