before I take the plunge with a hacksaw, does anyone here have a USE Carbon seat post that they have cut down. just want to check its not going to ruin it

Done handlebars but not a seatpost, but the principle's the same. I'd suggest a fine toothed blade, maybe even a decent junior hacksaw, and finish off with a fine wet-or-dry paper so there's no ragged edges left,

Make sure you're wearing a good face mask. You don't want to be breathing in any carbon fibre dust

Cool thanks guys. Here goes…!

Failing that get your hands on a plumbers pipe cutters & use them. Will give you a perfect cut once you use them carefully.

frank4short are you mental …. all that will do is crush the carbon….

Used mine to cut my carbon bars. Never had a problem just need to be very careful doing it. Quarter of a turn adjustment per revolution of the post works fine.