I have a kitchen with an existing exit door to the garden + a door to the hallway and an open space to the lounge. Can I replace the exit door with a window only? Thanks

If this is a question about means of escape in case of fire, then kitchens are excepted from the requirement for ground floor habitable rooms to have an escape route through a hallway or a suitable window. Mind you I'd think about making that replacement window suitable to get out of anyway (especially given my cooking abilities!).

Thanks, I thought it would be OK, and I will remember not to invite you around to cook, though. Cheers bud

It might be that you "can" but do you really want to?  If you sell it might put buyers off, especially if it became a long treck to the back garden.

 

Only do it if your kitchen is small and you really really need the extra bit of wall space created by turning a door into a window.