[llama]

Possibly using VGA might work but it wouldn't be a sustainable option for domestic reasons...
Quite reasonable objections, actually!
My feed to the projector is a single coax. It goes via the loft and that has given me an idea - point a video camera at a CRT TV in the dark in the loft. I think a flat panel TV up there would introduce video processing delay and muck up the lip-sync. Sounds a bit daft/surreal but it would certainly convert rented BT Vision films into the letterbox that would give me all the visual info without any geometry errors.

This afternoon I tried a Fresnel lens over the front of the projector lens in the hope that I could bend it slightly and if carefully done could provide the anamorphic effect needed. It didn't work - I think the lens had much too much magnification so the image was small on the screen and beyond the focus range of the projector's lens. I don't suppose a very low magnification Fresnel lens is available.

Maybe electronics is the way to go. (Or bite the bullet and get a more recent projector).
Graham