It was a home inspired by the finest neoclassical designs of the Scottish enlightenment at the heart of the London's richest neighbourhood. And now its remarkable contents are to go under the hammer.

Sotheby's later this month will auction the collection of Lord Ballyedmond, the Irish peer and multi-millionaire who died in a helicopter crash in 2014. The Ulster Unionist turned Tory was only the second politician ever to sit in the upper houses of both Britain and Ireland. And, as the second richest person in Northern Ireland, spent a portion of his £650m fortune on a unique collection of art and antiques.

Lord Ballyedmond, born Edward Haughey, turned a rundown property in Belgrave Square he bought for £12m in 2006 in to what was to be called “the Downton Abbey of our times”. Some 700 items, most from the home, based on the work of Edinburgh architect Robert Adam, will be sold.

Harry Dalmeny, Sotheby’s UK Chairman, said: “This collection is typically extraordinary; typical for an extraordinary man who accepted no boundaries in business, politics, art and friendship. Belgrave Square was where his ambition as a collector reached its zenith; this was the seat for a salon, where politicians and potentates from all sides of everything would find a home together at the dinner table.”

Lord Ballyedmond, Sotheby's said, transformed a once dormant property on one of London’s most prestigious squares into "a modern evocation of a great Georgian town house, specifically designed to entertain on an ambassadorial scale".

The auction house added: "The collection presented here was the fruit of selective and judicious collecting, both at auction and from dealers, with an unmatched attention to the finest of details. Paintings, tapestries, porcelain, silver and furniture were all thoughtfully put together to create something which would enthral and delight visitors to Belgrave Square."

Antiques are not just Adam-inspired but span hundreds of years and include a doll's house worth at least £6000 and Regency-era silver and porcelain tableware. They will be sold in late May.

Born in Dundalk in the Republic of Ireland, Lord Ballyedmond founded and ran Norbrook Group, a pharmaceutical company based in Newry, Northern Ireland. He was made a life peer for the Ulster Unionists but later defected to the Tories, who he also funded. Lord Ballyedmond also had A Georgian townhouse in Dublin, a castle in Northern Ireland and another castle in Cumbria.