The British will hold, a British-Soviet war in the 1980s.

This is something I am interested in.
I've done OBs / ORBATs before with a built-up British Armed Forces after having withdrawn intact from Western Europe and plotted out an Operation Sea Bear (as in Sea Lion) elsewhere before too.

This scenario of yours here is different. As in 1940, so much would be lost in a fight on the Continent. Britain would be in trouble faced with a continent in Soviet hands with the aircraft ranges of enemy aircraft a big deal, Scud/MRBM attacks and airborne assaults. Much of the TA was focused on NATO missions too and that was most of the better-trained units as well. Pretty much all of the available ground force's armour and artillery was to be sent abroad. What was left would be light infantry. Ulster could be stripped of troops and so too what was in Canada/Cyprus/Brunei/Hong Kong... but the country would be in dire straits.
Let me think some more on this.

The losses would be huge too, especially since there was the high state of readiness to move in those reinforcements therefore to get eaten up in your scenario. What might evacuate would be pitiful in the end in terms of numbers and certainly without much equipment, if none at all. It depends on how things would go though.

Canada and the rest of the Commonwealth would probably send either troops directly or volunteers.
The Soviet naval blockade would probably include warships but with British air power - even diminished - you'd probably be best going with submarines and aircraft for a blockade.

Was the alliance pre-war British dominated? Because Paris wouldn't stand for that! France has long been an equal to Britain.
I can understand a necessary agreement on British command during an evacuation across the Channel though the rumblings of discontent would be quite strong.
Inter-alliance politics & diplomacy would be a minefield.

Regarding the pre-war alliance being British dominated i do not think so, but the French did not have troops in West Germany, that is not until the Soviets had almost reached the Rhine but by that time even the French could not help step the Soviet tidal wave crashing across West Europe.

I presume not one Red Army boot touched French soil, otherwise the thermonuclear balloon would have gone up.

That sounds good.

Also was thinking with the United States going back to being isolated from the outside word and before the outbreak of the Euro-Soviet War the British replaced the Americans in South Korea with the British Army of Korea.