Thanks for clarifying that this is just risk estimation based on not knowing what the outcome is. There is also a risk in not including UK institutions- they have some mighty fine researchers there, so not including them might lead to a project not being approved (for lack of continental experts in a specific topic) or being unsuccessful (for lack of execution capabilities).

It's trading a well-understood risk for a one that is not well-understood, hence my comment about it being irrational.