A rare document signed by Norfolk's Lord Nelson has sold for more than £20,000 at auction – double the expected price.

The Burnham Thorpe-born naval hero's signature was on the marriage certificate of Norfolk couple William and Anne Bottalin.

The pair had been living in Naples at the time of their wedding in July 1799, when Lord Horatio Nelson signed the form.

Eastern Daily Press: Lord NelsonLord Nelson (Image: Archant)

They got married aboard Nelson’s ship HMS Foudroyant in the Bay of Naples in July 1799.

Experts said the document provides a unique snapshot into a particularly complicated period in Nelson’s personal life against a backdrop of great public triumph.

Lord Nelson was a household name in Britain due to his many victories, including the Battle of the Nile against the French Navy in August 1798 – which came before the Battle of Trafalgar in 1805.

He had an affair with a former courtesan, Lady Emma Hamilton, who became pregnant with his only child. Her signature is also on the marriage certificate.

The single sheet of heavily autographed paper, which had been in the same family for 222 years, was sold as part of an auction of rare books, manuscripts, maps and photographs sale in Edinburgh on Wednesday.

Eastern Daily Press: The Battle of Trafalgar by JMW Turner. Pic: Tate LondonThe Battle of Trafalgar by JMW Turner. Pic: Tate London (Image: Tate London)

A first edition of JK Rowling’s Harry Potter And The Philosopher’s Stone also fetched more than £20,000.

Simon Vickers of auctioneers Lyon & Turnbull said: "The results of this sale demonstrate the current strength of the market for rare and important books.

"The marriage certificate was completely new to market and had been in the family of the married couple for over 200 years. We were delighted to see it sell for £20,160."

Dominic Somerville-Brown, a Lyon & Turnbull specialist, said: "We know of no other such document, bearing the signatures of such a spectacular array of characters in the Nelson story, ever coming to market."