He would go on to write The Rime of the Ancient Mariner and Kubla Khan, two of the greatest English poems.

But in a letter written when he was 22, Samuel Taylor Coleridge revealed he was contemplating packing it all in and fading into obscurity.

The letter, which is being offered for sale by the London rare books and manuscripts dealer Bernard Quaritch, details his low mood and disappointment in love, and appears to allude to an opium addiction.

The young Coleridge writes he is finishing a work of “consequence”, believed to be his long philosophical-political poem Religious Musings.

But he adds that he is planning to “bid farewell forever” to the stress of writing. “I mean to retire into obscure inactivity, where my feelings may stagnate into peace,” he writes.

Donovan Rees, the head of English books and manuscripts at Bernard Quaritch, described it as a “sliding doors moment” for Coleridge.

Rees said: “If his friends hadn’t stepped in at the right time, and taken him off to Bristol and to his future meeting with William Wordsworth, it is entirely possible his genius would never have revealed itself, and that his depression and laudanum addiction could have led to a very different fate.

“Certainly on the basis of what he had published up to that point he would have only been a footnote in the history of English poetry.”

The letter was written to his friend George Dyer, a leading English radical who championed the young Coleridge, in January 1795, shortly after he left the University of Cambridge.

It almost certainly alludes to Coleridge’s infatuation with Mary Evans, with whom he had been in love since his schooldays. The news of her engagement to another man brought “bitter disappointment” – as he puts it in the letter.

In what may be allusions to both lost love and opium, he says in the letter: “My delirious imagination had early concentrated all hopes of happiness in one point – an unattainable point! This circumstance has produced a dreaminess of mind, which too often makes me forgetful of others’ feelings.”

He thanks Dyer for “a very flattering review of a very indifferent composition of mine”, The Fall of Robespierre, a three-act play that Coleridge and Robert Southey wrote with the intention of raising funds for “pantisocracy”. This was a scheme to found a commune in rural Pennsylvania with 12 men and 12 women who would marry and bring up their children in an equal society without private property.

Coleridge is deprecating about some of his first poems, published in the newspaper the Morning Chronicle, though writes that two are “not so bad as the rest”.

Soon after writing the letter, he headed to south-west England and met Wordsworth. In 1798, the pair published a joint volume of poetry, Lyrical Ballads, considered to be a starting point for the English romantic age.

A standout in the collection was Coleridge’s The Rime of the Ancient Mariner. In 1797, Coleridge put his quill pen down on the wondrous Kubla Khan, which he apparently wrote after experiencing an opium-influenced dream.

Rees said it was possible Coleridge was being a little dramatic in the letter. “There is clearly an element of performance – Coleridge is writing to an older and more experienced man whose opinion he very much respected.

“I think we see two sides of Coleridge here. He is both fishing for compliments and yet also self-critical and not satisfied with what he has written so far.

“Luckily Dyer does seem to have risen to the occasion and provided Coleridge with enough encouragement that he didn’t retire into obscurity. His was a candle destined to burn bright and hard, not to fade and gutter.”

The Coleridge letter, which has a price tag of £10,000, is one of 80 items in Bernard Quaritch’s new catalogue of English books and manuscripts from 1500 to 1840.