Almost 28 acres on the edge of the Phoenix Park at Castleknock, Co Dublin, left, bought last summer by the country's largest housebuilding company, Menolly Homes, could prove to be the most valuable housing site close to the city.

However, the new owner will first have to persuade the members of Fingal Co Council to vote in favour of a material contravention of the development plan, in order to allow the site to be developed. Menolly paid around £25 million (#31.75 million) for the land and three houses, which were owned for many years by the Guinness family.

The land had provided a buffer for the family home, Farmleigh, until it was sold almost two years ago to the Government for £23 million (#29.21 million). Menolly is likely to seek planning permission for up to 450 housing units; about half of them high-value detached houses, and the remainder large apartments. The most sought-after houses will undoubtedly be those which are to be built on a narrow strip of land running along White's Road to what is now a pedestrian entrance to the Phoenix Park.