Regarded as the first written constitution ever produced in the English-speaking world, a rare publication of Oliver Cromwell's Instrument of Government is coming to auction in London.

Cromwell's Instrument of Government legitimised his power

A fascinating document from the only period in which the country has not been ruled by a monarch, the 259 by 169mm specimen is expected to sell for up to £5,000 ($7,964) when it auctions at Sotheby's English Literature, History, Children's Books & Illustrations sale on December 12.

Drafted in 1653 by Major-General John Lambert, it came into effect in December of that year as Oliver Cromwell became lord protector and officially gained control of England, Scotland and Ireland.

The document bears the contemporaneous printing date of 1653, further enhancing its value.

"The Instrument was intended to provide a legal basis for government after the parliamentary failures of the civil war; its immediate effect was to legitimise the power of Cromwell and his generals," says Sotheby's.

It was superseded just four years later by the Humble Petition and Advice, an example of which is also selling at the auction, with a £3,000 ($4,778) estimate.

2012 has already witnessed strong performances for Cromwellian documents.

A manuscript announcing Cromwell's official abolition of the British monarchy in 1649 sold for £13,750 ($22,000) in July, beating its £5,000 high estimate by 175%, while another document, proclaiming the cancellation of Christmas, achieved £5,625 ($9,000).

The sale will be highlighted by a rare £200,000-valued edition of Jane Austen's Emma. We will bring you full results here at Paul Fraser Collectibles next month.

View this historically-important English document you can buy today.