The script for Nitty Gritty, an unmade BBC sketch show written by John Sullivan, is due to be sold at auction later this month.

Described by auctioneers as a bridging gap towards Only Fools And Horses, the single 65-page script was penned early in 1978 and sent to a fellow writer, Alan Wightman, as a sample for a prospective collaboration.

Bristol auction house Auctioneum will put the item - complete with covering letter from Sullivan - under the hammer on Thursday 29th February.

Auctioneer Andrew Stowe says: "This is an incredible discovery, and an important piece of comedy history. Only Fools And Horses is Britain's most popular sitcom and to discover some new work from John Sullivan is like finding a new play by Shakespeare, or a new novel from Charles Dickens!"

The script appears to have been penned in-between Series 1 and 2 of Citizen Smith. 1977 was Sullivan's break-through year, when he first had material aired in hit sketch format The Two Ronnies, and debuted Citizen Smith, a sitcom of his own creation.

The covering letter explains that some sketches are unfinished, but the script should give an outline of Sullivan's vision for the programme. It also suggests that he had already broached the concept with the BBC, who were interested in the format and encouraged him to write it with a linking theme between each sketch.

Stowe explained: "It's undeniably Sullivan. The themes in the sketches are instantly recognisable as his work.

My particular favourite sketch is titled The Lament Of The Cowboy From Balham, and was likely proposed as musical number. It features imagery of 1970s London, and is clearly largely auto-biographical as Sullivan grew up in Balham. The 'nitty gritty' of London really shines through in the piece, something that he would later rely on in Only Fools And Horses.

"Real people, real life, funny stories. This script was Sullivan bridging the gap between sketch show and sitcom and is a very exciting discovery."