Pictures of before and after, proposed door replacement.

Hi all,
The first picture shows my current work in progress house. The plan is to replace the back door by extending the window, as per the second pic of a neighbour's house.
[/URL]
Does anyone have any knowledge on the construction of these 1970s houses? Would I need to brick up the hole left by the bottom of the door, or are the "walls" of these houses stud walls, covered by flashing/fascia? I presume the current window/door frame is offering no structural support to the building?
Also, I'm a competent DIYer, but never fitted a window before; is there legislation for windows to be done by a professional these days with a certificate given?

 

Oh really? Interesting, thanks.