The 1980 Lyceum gigs were 6 & 7 May, so if you mean 7 May (the one famously filmed by the BBC for Whistle Test) then you and I were at the same two gigs, as I also went to the Hammersmith Thu 27 March one. That was the first of 3 shows at Hammersmith, they did The Knife on the 3rd of those. But otherwise yes the only encore was IKWIL.
you are, of course right, I was at the second Lyceum gig, which was on the 7th. At Hammersmith we got BINYC, which was then replaced by Squonk, iirr.