You’re actually the first to ask! I think that it’s Jonny’s Korg Prophecy, with liberal use of log controller for pitch plus distortion.
From its glissando, it seems likely that it could be his Korg Prophecy, especially since on listening now I notice that a synth was used quite a lot on the song. It could be his Moog Rogue, but he might not have had that yet, although the filters do sound sort of Moogish.
I think that it’s the Prophecy into some sort of distortion. It might be onboard distortion, or it might have been run into a pedal and/or guitar amp.
Itcould be an excellent use of the Rogue’s glide feature, with the synth running into some sort of distortion, but one of the Prophecy’s major points is its log controller which Jonny used for Ondes-like sounds in the late 90’s.