cutting stainless steel cooker hood?

Jigsaw, fine metal blade, and masking tape (to avoid any scratching). Worked fine on mine. Do a test cut on the scrap (i.e. the bit you're cutting off) first. Do make sure you correctly identify which side is scrap :)

Ok first section of the chimney has been done, I got a very straight and clean edge, and very little filing required to smooth the edges. I did a test cut on the waste first though. I used a jigsaw, fine metal blade. I marked up the cut line and then used masking tape to further identify the line. On either side of the cut line I sellotaped 3 thickness of newspaper to avoid scratches. I then packed the inside of the chimney with boxes, wedges, anything to make it more stable, from both sides so as not to interfere with the blade on the cutline. I then using gaffa tape attached a piece of wood to act as a guideline in case I wandered off. When I came to cutting the fourth side I gaffa taped the other 3 sides across the cut to stop any additional vibration etc. All in it probably took me about an hour with packing,taping and cutting. More than happy with the result. Pictures avaliable if anyone requires them.

Thank again to all who offered suggestions.

A hacksaw won't be able to physically fit into the position required once you get part-way into the cut.

I cut down the chimney section of my SST cooker hood using the cutting disk of a dremmel. Was quick, clean and accurate. Mark it out carefully first.