All the nasty/embarrassing stories for UK will be resurfaced to weight in Brexit negotiations. Russia already warned the international community that UK didn't cooperate well about all the accusations of nerve agents (not that Russia cooperates massively either).
Personal opinion : UK gov thinks they are the only people on Earth, they think they can ignore their neighbors, they overestimate themselves and I hope a bad Brexit will give them a good lesson. If UK were a passive country and actually self-sufficient, we wouldn't care much. But they actively try to influence international relations, and they want to do it without EU, which is obviously egoist and short-sighted, since they don't get to chose their geographical neighbors.
Personal opinion : UK gov thinks they are the only people on Earth, they think they can ignore their neighbors, they overestimate themselves and I hope a bad Brexit will give them a good lesson. If UK were a passive country and actually self-sufficient, we wouldn't care much. But they actively try to influence international relations, and they want to do it without EU, which is obviously egoist and short-sighted, since they don't get to chose their geographical neighbors.