Nothing came of this. From the Guardian:
As Bolton, a former US ambassador to the UN, ended his hour-long discussion at the Hay festival, Monbiot, who had earlier challenged him for alleged breaches of the post-war Nuremburg Principles, moved towards the stage waving a charge sheet.
But security staff, alerted by pre-publicity, intervened and bundled Monbiot out of the tent as 20 supporters chanted “war criminal” and waved placards. The comedian, Marcus Brigstocke, who tried to pursue Bolton as he left the other side of the tent, was also blocked by security staff.
How sadly anti-climactic.