Tycoon David Ross, who made his fortune by co-founding Carphones Warehouse, is selling the 1,500 acre estate at Brampton Ash where his stepsister was murdered.

In April 2006, Fiona Marshall and her lover, Richard Flippance, were stabbed to death by her estranged husband, Alex, who then set fire to the bungalow in a bid to destroy evidence.

Fiona, aged 41, and her 44-year-old boyfriend were stabbed to death and the building then destroyed in an explosion.

Marshall, aged 38, is serving two life sentences for the murders, with a minimum of 30 years, after he was convicted by a jury at Birmingham Crown Court.

The killings are said to have deeply affected Ross, who was close to his stepsister, and is thought to be the main reason he is now selling up.

He has instructed Market Harborough agents, Fisher German, to sell the estate, for which he paid around £3 million in 2002.

A spokesman said: "We are asking for offers in excess of £7.75m, which reflects the current agricultural land price of about £6,000 per acre."

Until the late 1980s, Brampton Ash was owned by the Spencers, Princess Diana's family, who also own Althorp near Northampton.

It includes extensive woodlands and a shooting lodge as well as 1,460 acres of farmland. Under Ross's ownership, he has overseen shoots with guests including Sir Richard Branson, former MP Winston Churchill and Gary Lineker.

The Tory donor bought two prestigious grouse moors in North Yorkshire and it is believed he plans to use the sale proceeds to invest further in these estates and focus on his 2,000-acre Nevill Holt estate, six miles from Brampton Ash, where he owns a grade one listed mansion.

A close friend of bachelor Ross told The Daily Mail: "David has bad memories of Brampton Ash because of Fiona's murder. The estate used to be the jewel in his crown. Now he's fallen out of love with it."