German domination of continental Europe does pose a potential long-term threat to Britain, at least until the Americans come in. It's why Britain has always committed itself to wars designed to prevent such dominance by any single continental European power.
Several of our estemmed British members have repeatedly pointed out that the UK`s "policy" to prevent continental hegemony is rather overstated on this board. It did exist, but it was not the cornerstone of British strategic thought as it is sometimes described.
Actually it is indeed the other way around: making peace with the power which is not much of a threat to either the British homeland or empire to free up resources to focus on the struggle against the power which actually is a threat to those things is a perfectly sensible thing to do.
It`s still a backwards line of thinking. Surely it makes more sense to make peace with the power that actually threatens you, and thus actually ending the whole war! That way you free up all the resources for round two.
A semi-phony war which isn't going to see much in the way of large-scale fighting.
You don`t really need Barbarossa or Bargation to make an impact on the wider war.
Neither the USSR nor British really have the logistics in the region to make the requisite a major offensive out of or into the Caucasus.
They seemed to manage the invasion of Iran well enough.