Is this song about rape?

Joan Armatrading is one of my favourite and only recently-discovered-by-me artists. She is a black, female singer of incredible vocal prowess who writes beautiful, moving and articulate songs, displaying an economy with words found among the very best songwriters.

The lyrics below are for Water With the Wine, which you can listen to here. The music for this song sounds happy, cheerful and celebratory. It was only today when, for whatever reason, I really listened to the words that I picked out "got no strength to make him stop" that I was thrown.

Met him on a Monday
And he said he loved me so
Walked me to my door
Before I knew it to my living room

I thought there was no need for worry
When he took me in his arms
Drank some whisky
Hung his coat upon the stand

That's when the music started
I heard the light switch click
I stumbled on a lost shoe
The fever's starting

This man was getting hot
I got no strength to make him stop
I guess it's too late
But I'll know next time
To mix some water with the wine

The sun came pouring in at five
Upon my face
I felt the taste of last night's love
Upon my lips
I wasn't sure if I had dreamt it
Or had not
But there across the pillow was the face
I had forgot

That's when he said he loved me
Could be the truth this time
He put his arms about me
Fever's starting

This man was getting hot
I got no strength to make him stop
I guess it's too late
But I'll know next time
To mix some water with the wine

So my question is, is this song about rape? Or at least, about sex someone doesn't really want but feels unable to prevent, which many feminists would class as rape? Or is it deliberately ambiguous? Is she just messing with my mind, writing a song with a chorus in a major key so that it sounds feelgood but actually isn't?

Ok, so this isn't one of life's Big Questions^TM, but still, I wondered.