Billionaire businessmen John Magnier and JP McManus could finally secure a bumper payday on their 2013 purchase of “high amenity” Liffey Valley lands for just over €4 million through a housing rezoning proposal backed by the chief executive of South Dublin County Council.A plot at St Edmundsbury on the southside of the river Liffey, close to Lucan and just west of the Hermitage Golf Club, which has been protected from development for decades, could accommodate more than 500 homes, according to a submission to the council from the O’Flynn Group, development partners of McManus and Magnier.The horse racing, property and international investment magnates in 2013 bought 110 hectares of land, previously owned by Sean Mulryan and Marese Ltd, for €4.3 million at an auction ordered by the National Asset Management Agency (Nama).Successive attempts, by the group and previous owners, to rezone the land for housing have been repeatedly rebuffed by the council due to the land’s exceptional environmental and natural amenity value, and because sufficient sites had already been rezoned in the Lucan area for housing.However, following an edict last summer from Minister for Housing James Browne that all local authorities must rezone significant additional land for housing, the council’s executive Colm Ward is recommending councillors rezone approximately 16 hectares at St Edmundsbury.These lands represent just over 10 per cent of the 156 hectares the council has identified for rezoning, with other plots proposed around Adamstown, Citywest and several established suburbs in south Dublin. However, of the 2,678 submissions made on the proposals, 60 per cent were objections to the rezoning of the St Edmundsbury lands.Lucan locals described the move as “unthinkable”, “baffling” and “an absolute disgrace”. The Liffey Valley Park Alliance said while individual developments “may appear limited in scale, the gradual reduction of green areas over time can lead to a significant loss of ecological connectivity and landscape character”.Independent councillor Helen Farrell said she was “appalled” by the proposal and the land should be acquired by the State. Independent TD Paul Gogarty said housing estates at St Edmundsbury would be “an absolute abomination”.In their rationale for the rezoning, the planning consultants for the O’Flynn Group, McCutcheon Halley, said the 16 hectares “do not form part of an undeveloped valley floor landscape but rather lie directly adjacent to institutional landscape at the urban edge of Lucan” and the new zoning ensured housing would be accompanied by a “park delivery strategy”. In his report on the submissions, Ward said a “park is required to be provided in tandem with, or before, any residential development, ensuring that the sensitive and strategically important lands within the valley are secured, protected and enhanced at the earliest stage”.The rezoned land “represents a relatively small proportion of the overall Liffey Valley and has been carefully defined having regard to the sensitivity of the wider landscape”, he said.In a statement, Michael O’Flynn, O’Flynn Group chief executive, said “Edmundsbury is the perfect location for new homes” and “contrary to some assertions, our plans would enhance accessibility to the riverside green space and strengthen rather than diminish public access and recreational opportunities within the area”.Councillors will vote on the rezonings next month.