I'd think you'll have trouble selling it even for £200. Unless the buyer is oblivious of technological advances, and only sees "120Hz", "240Hz" and "gaming monitor".
But bear in mind, that monitor is almost four years old. In essence, it was released before the 120Hz+ IPS panels became mainstream, and before the VA panels started gaining against IPS. Since then, both IPS panels and VA panels have progressed in terms of size, resolution, refresh rate and lag. And most importantly, adaptive sync technologies. Against today's gaming monitors, it simply doesn't hold its ground.
It is an Eizo, though. Eizo is more of a premium brand, so those maintain their value slightly better. You could indeed try £300 and see whether some unfortunate soul takes the bite. But if you want to move it faster, you need to set a more competitive price, probably £200 or maybe even £150.