It is a 406 1.8l8v 1999 T reg saloon any help greatly appreciated

turn up the radio !
you details are shorta vague.
check your fuse ? is it connected ?somtimes things get shoved in widows where it connects.

Use a 12 volt ohmmeter to see if any electricity is flowing between the ''metallic paint stripes'' on the glass. Look for the main connection to the grid, near the window frame.
My guess is that a tiny scratch on the main connector prevents electricity from flowing to all lines. A tiny scratch on just one line would only prevent that one line from working.

Years of strong sunlight have faded & flaked the metallic paint on my connector. l bought a small jar of this paint in America, because l have never seen it for sale in Belgium.

PS. of course u have already checked the fuse. but there is also a relay on this circuit as well. Peugeot has added rear window defroster relays since 1986. Find it too.

Assuming the fuse is OK, check for any brakes in the metallic element. You can buy a small bottle (nail varnish size) of metallic paint specially for repairing broken heated rear windows. l got some from Halfords but l am sure other motor factor shops will sell it. It is quite expensive! about £5 or £6 a bottle!

Trade you car for another make that has working electrics.