Zinsser Bullseye 123 primer & sealer (white Matt, about 1 litre)
I brought a 2.5 litre tin of this primer for my decorating job and there is now about 1 litre left in that tin which I don’t need. The 2.5 litre tin was purchased for £37 so 1 litre for £15 is a bargain if you only need that much