It's not unusual for competing empires to consider temporary power-sharing deals like that so they can divide the world up into their own spheres of influence and not have to fight one another. It happens frequently, but it usually onlys last for a relatively short period of time. Why be so astounded that someone in Great Britain would come up with that idea vis a vis the Uk and Germany?

Stalin came to a temporary meeting of minds with the Germans, for example...long enough to assault Finland and gobble up various other territories in the west, including a large hunk of Poland.

The agreement held until Germany's attack on Russia in '41, despite the fact that the Russians and Germans did not like each other's regimes one bit. Nothing works like mutual survival instinct coupled with a desire for material gain.

As long as the plan suits both parties, they will back it.