It's possible that the plastic handle was moulded round the steel saw plate, then fitted with screws, so it may be firmly stuck.
You could cut through it with a hacksaw - I assume you didn't want to keep the handle?
If you don't want to replace it - and I doubt if the saw deserves a new handle - just leave the handle in place. There is no need to remove every saw handle just to clean rust off the blade.
Hi Fumbles, if it were me I would put the screws about half to two thirds of the way back into the nut and place the nut over the void in a slightly open vice. A light tap or 3 with a non marring hammer or a block with any old hammer should convince the nuts to move some. repeat until freed.
And just to add...if you don't want to use it as a saw or practicing sharpening....you could make a few scrapers out of the steel or cutters for scratch stocks.
Never throw anything away...scrapers are not cheap!
More than likely they have used press fit hollow pins to secure the blade to the handle. These pins have an internal thread which are sized to mate with the external threaded saw screws. Without destroying the handle These pins are very difficult to remove.
I pulled apart a similar built modern backsaw that had a wood handle.
You might be right Stewie, they could have used used cutlers' rivets. However, Fumbles said he took the screws out. The question is whether he's willing to risk damaging what looks like a heritage piece of plastic. :wink:
By the way Fumbles, is that a Spear and Jackson?