1. We have secure lines of communication as USSR has no maritime capability.
2. We have jet fighters albeit short range, high performance prop fighters, long range bombers, radio navigation aids, and probably air superiority if not supremacy.
3. The army is numerically inferior and its tanks, whilst numerous are out numbered and outgunned.
4. A scorched earth policy and a devastated 3rd Reich deny the Red Army opportunistic logistic supplies.
5. The Red Army loses manoeuvre ability.
6. Red Army has slow advance and continuous interdiucy and attrition.
But
7. A thrust into Caucasus oil fields and Persia and Iraq secure oily supplies and deny these to British forces.
8. Red Army reaches North Sea but lacks any ability to reach UK.
9. British Army retires in good order to UK.
10. RAF jet bombers continue deep penetration raids into eastern Europe.
11. RN units blockade Dardanelles and Baltic.
End game, Reds hold northern Europe. UK controls all SLOC and Air Supremacy to Russian border.