As shown in the title, I read this in the very early 1980s. I think it was a Brit author. I thought of it yesterday after the BBC controversy about 'Last Night of the Proms'.
Somewhat like SS-GB in that it gives the story from the viewpoint of a conquered country desperately trying to get the USA involved as an ally.
I can't recall exactly how but Britain is overrun and being assimilated into the Iron Curtain, I think it was set in the 1990s but obviously the writer (in the early 1980s) never envisaged the collapse of the Soviet Union.
There were scenes describing a liaison attaché who has to cooperate with one of the conquerors. The Russian is very interested in how the Open University works and they intend to set similar up in the USSR.
During the occupation there is a dockworkers strike, I think it was at Liverpool, the Russians do a 'conquered Berlin' reprisal where they send in the shock troops. For a few days they run wild, shooting men at random and raping females. I remember the weeping with rage liaison guy shouting at the Russian officer about they'd never forgive him for all those wives and daughters.
The Russian high ups attend the Last Night of the Proms and get very irate at all the Union flags being waved and everyone singing Land of Hope and Glory. Video footage of previous years convince them it's a long standing tradition.
Another scene, liaison attaché and Russian officer .... This could still be at the Proms. As they talk two oldish men walk past them unrecognised, it's George Harrison and Ringo Starr.
I don't recall anything else, a vague feeling that somehow the Russians are forced to leave - maybe a UK nuke sub skipper ignores orders to hand over his vessel, instead he threatens to launch (this faint memory might be a different story).