This is Eilean Aigas, arguably one of the finest country houses to be built in Scotland this century. Set on a private island within a large Inverness-shire estate, it will be sold at auction on 21st September – unless a buyer secures it with an 'acceptable offer' in the meantime.

The first house on the island was built in 1839 by Lord Lovat for the Sobieski Stuart brothers who claimed – fraudently – to be direct descendants of Bonnie Prince Charlie. Later in its history, Conservative statesman and prime minister Sir Robert Peel used it as a summer retreat; writer Compton Mackenzie rented it for a period in the 1930s.

The present owner bought Eilean Aigas in 2003 and set about building a new house on an epic scale, comprising half a dozen magnificent reception rooms and eight bedroom suites. Working with a team of expert craftsmen, it took six years to create a house that looks as if it has evolved over several centuries.

The original house has also been renovated and a new gate lodge and estate office with staff accommodation have been added. There is a further farmhouse with development potential.

Surrounded by 500 acres of woodland and farmland, the island is totally private, though it is actually remarkably accessible. The nearest village, Beauly, is around three miles away; Inverness is around 14 miles and the airport, with direct services to London Luton and Gatwick, Edinburgh, Manchester, Birmingham, Bristol and Amsterdam, around 24 miles.

The auction is likely to attract a great deal of national and international attention and the price on the day will be determined by that interest. But a motivated buyer could prevent Eilean Aigas from reaching the auction by purchasing it by private treaty this summer. Clearly, a pre-emptive bid would need to reflect the incredibly high standard of craftsmanship that has gone into the house as well as its idyllic location – certainly in excess of £3 milion.