Recently brought a flat that has a lowered ceiling(image 1) part of way down window. Wondering if this would of been done for fire regs, and whether I could put new full length windows in and raise the ceiling on an angle around them. This is a ground floor flat in a converted property. Thanks. 

I would suspect this is the person lowering the ceiling and insulating it thermally/sound, it doesn't appear to have anything to do with fire safety, quite the opposite I would think.