Less well known, however, is the original version of the song, released four decades ago this year, on 1 July 1985. Its UK chart position of 116 probably reflects the less punchy production. The accompanying music video is a choice example of a genre which, in the 1980s, often looked like the costume department had been raided by a drunken mob and the choreography led by someone on LSD. In a car park, Neil Tennant is standing in a manhole dressed in a designer suit, glasses and Homburg. Behind him is a Cadillac with its headlights on. What on earth was the song’s ‘dodgy geezer’ lead character doing with his head sticking out of a hole in the ground, and why was there a car behind him, apparently waiting to run him over? Even more inscrutable was the video’s ending, which accompanied the original song's forgotten coda.

As the music comes to a dramatic stop, leaving only the drone of the final chord, we watch Neil Tennant dissolve. All that's left afterwards is a clothes hanger, holding his suit jacket and shirt; then the clothes hanger and clothes vanish, and the Cadillac drives over the now empty hole and out of shot. The sequence is accompanied by Neil Tennant intoning: ‘All the love that we had and the love that we hide / Who will bury us when we die?’ If the song was sardonic and the video absurdist, then this was an abrupt tonal shift into something altogether darker.

In a 2009 interview with OUT magazine, Neil Tennant described the moment AIDS first entered his life, and how it inspired the song, ‘It Couldn’t Happen Here.’ ‘My best friend was diagnosed with AIDS in 1986,’ Tennant explained, ‘and that song is a description of a conversation we had. I remembered him saying in the very early days that AIDS was not going to happen in Britain for various reasons. And we were being a bit complacent about it.’ Pet Shop Boys would go on to write a number of songs about AIDS, the most poignant perhaps being ‘Your Funny Uncle’, inspired once again by Tennant's personal experience. At the funeral of the best friend who had died of AIDS in 1986, Tennant noticed the deceased’s uncle looking around at his nephew's gay friends and piecing the cause of his death together.

As the 1980s ran on into the 1990s, education began to dispel the ignorance and pop songs’ once vague references to AIDS became clearer. By 1990 Neneh Cherry’s ‘I Got You Under My Skin’ included the lines, ‘Caught by a plague slowly they fade / From immune deficiency you see called AIDS.’

But this was the summer of 1985. At Live Aid that year, as the whole of Wembley Stadium did the double handclap during Queen’s ‘Radio Ga Ga’, Mercury looked back at the audience having already experienced symptoms associated with HIV. It was a time when misunderstanding generated huge amounts of fear, when the HIV virus was still referred to as the ‘gay plague’ and ‘gay cancer’. No wonder Pet Shop Boys’ brief spoken word piece was hidden away in a coda. For a duo who so often seamlessly blended irony and sincerity, this was a rare example of straightforward honesty.

Scholarly articles and academic tomes might best remember history’s complexity, but songs recall the past’s emotions and moods with visceral power. Whether it be Noel Coward’s Jazz Age songs, the Beatles’ Summer of Love anthem, ‘All You Need Is Love’ or Pet Shop Boys’ ‘Opportunities’, there is an unofficial list of songs which soundtrack the history of 20th century Britain. And the coda to the original version of ‘Opportunities’ should be added to the inventory as an important footnote. ‘All the love that we had and the love that we hide / Who will bury us when we die?’ It testifies to the gay community’s fear and helplessness during the early years of the AIDS pandemic, when all around it was ignorance, hate and hostility.