The windows are tilt & turn (with a non-opening panel at bottom due to their large size) with 2 panes 60mm glass & 20mm space in between (not vacuum - chap said that's all just sales patter, you can't have a vacuum as glass is porous). Sills would be mahogany. No deposit required. He seemed reputable; he wanted me to sign up then and there but didn't push it. He said VEKA are brilliant quality but of course I don't know.... Price quoted £7.7K (I think that's inc VAT). He said WeatherSeal (who quoted £5K) don't fit very well and may not use the specs of window that they showed me in their sample... I think I believe him.
Any thoughts you may have would be (very) gratefully received.