You can hear the song here (embedding was disabled for that video otherwise I'd put it here). Here are the lyrics for the song along with my specific reasons why it refers to Churchill:
History recalls how great the fall can be
While everybody's sleeping, the boats put out to sea 
Borne on the wings of time
It seemed the answers were so easy to find 
Too late, the prophets cry
The island's sinking, let's take to the sky 
Called the man a fool, stripped him of his pride
Everyone was laughing up until the day he died 
And though the wound went deep
Still he's calling us out of our sleep 
My friends, we're not alone
He waits in silence to lead us all home 
So you tell me that you find it hard to grow
Well I know, I know, I know
And you tell me that you've many seeds to sow
Well I know, I know, I know 
Can you hear what I'm saying?
Can you see the parts that I'm playing?
Holy man, rocker man, come-on queenie,
Joker man, spider man, blue-eyed meanie 
So you found your solution
What will be your last contribution?
Live it up, rip it up, why so lazy?
Give it out, dish it out, let's go crazy! 
 Refers to Francis Drake's night time attacks to fend off the Spanish Armada in 1588.
 Refers to the British Empire's subsequent historical momentum and a sense of entitlement.
 I've no idea who the "prophets" were of the time but their message was to abandon the ship of state.
 Refers to the replacement of Churchill by the Labour Party and the subsequent decades-long deconstruction of his legacy (note that this song was written in 1977, prior to the ascendency of Thatcher).
 &  Here is where the allusion to a force from beyond (ostensibly the memory of Churchill) may have caused that Althouse commenter to remark that he thought the song was about Jesus.
 Here the songwriter is answering the unspoken retort from British youth--that maturity is hard, that the legacy is too hard to live up to.
 Refers to the spectrum of people present in the 1970s Britain: religious, culture, celebrity, social, misfit--each one is a character.
 Refers to the state of anarchy amongst the mid 1970's youth in Britain.