It is an instantly recognisable pop song all around the world.

But now a Sussex poet has cast a cloud over the authenticity of David Bowie's 1977 single Heroes, claiming the flamboyant musician plagiarised the lyrics from her writing.

Shuna Shelley, from Worthing, said she sent a poem called The Heroes' Epistle to Bowie in 1974, partly as an expression of her enthusiasm for his music.

She was a fledgling singer and songwriter who was finding it hard to make her mark without being in a band, a virtual impossibility with four young sons.

She had passionately followed the careers of doomed Sixties icons Jimi Hendrix and Janis Joplin and feared Bowie might also succumb to the allure of drugs and hard living.

She clipped a postcard of 13th Century Italian poet Dante, and Beatrice, the object of his boyish affections, standing near a wall to the first page of her poem.

Bowie has said the wall mentioned in his song Heroes was the Berlin Wall, and the lyrics encapsulate the spirit of two lovers standing beside it.

Mrs Shelley said The Heroes' Epistle, which she asked her husband to hand deliver to Bowie's Kent address at the time, included the words: "We, we can be heroes/Just for our day/I, I will be king/And you/You will be my queen/And I wish/I wish you could swim/Like the dolphins, like dolphins can swim."

Bowie's celebrated Heroes, which recently formed the background music for a Microsoft commercial, has the words:

"I, I will be king/And you, you will be queen/We can beat them, just for one day/We can be heroes/Just for one day/I, I wish you could swim/Like the dolphins, like dolphins can swim."

She said she has never received any recognition from him.

Now aged 57 and suffering from the chronic fatigue disorder ME, Mrs Shelley has started the legal process of claiming what she sees as her rightful credit.

She was previously put off because of poor health and the fact it seemed such a daunting task to take on one of rock music's giants.

Mrs Shelley said: "Heroes has become his anthem. I have to listen to it on the radio and hear it on commercials. This is about ethics as much as it is about claiming any money. I didn't know about copyright. I just wrote the poem."

Bowie's lawyers have refuted Mrs Shelley's allegations.