Is correct fill expanding foam when there are at least 3-5cm gap between window frame and the wall?

Hi, Certainly not the best practice if the window is fitted between the bricks (brick to brick aperture), but was this fitting behind the facing brick / stonework, where the face of the frame meets the back of the masonry (fitted in check)? Did you see the gaps externally or internally (to the internal plaster)? This would give a better indication as to how the windows were fitted. If it is 'brick to brick', the sizes of the gaps you have given (15mm - 50mm) are very excessive to then be foamed and sealed. (Although it's worth noting that sometimes you need to look to see if the aperture is completely square. If it isn't, then larger gaps can occur. Obviously a completely true manufactured window, running perfect 90 degree right angles, isn't always going to fit perfect in an opening that is running out). If it is 'In check' and the gaps are internal up to the plaster, then this is acceptable, but would need DPC to sides prior to foam filling, cloaking with architraves then sealing. Also the cill isn't always fixed to the window prior to fitting. As long as there's a bead of mastic sealant between the window and the cill (before being screwed together) the cill is sealed underneath between the masonry and the cill, and finally the ends are closed off with mastic to stop any water transfer, it should be fine (although this is just in reply to your description and obviously have not seen the window!). Hope this helps.