There are not many truly excellent Modern buildings in the UK. And there are even fewer in Northern Ireland.
One rare example is the extension to the Ulster Museum in Belfast, credited to architect Francis Pym, which is a beautifully mannered Brutalist addition to the 1930s original.
But how much longer this Grade B+-listed building will remain in its current state is the subject of fevered debate after a planning application to make significant changes was lodged by the museum authorities with Belfast City Council at the end of last year.
Significantly, the proposals, by local practice Hamilton Architects, have the backing of Northern Ireland's Environment and Heritage Service (EHS), the province's equivalent of English Heritage.
The plans, which some supporters are simply describing as a renovation, will, in fact, totally transform the building, which was the only project completed by Pym before he retired from architecture to become an Anglican priest.
The changes - backed financially by the Department of Culture, Arts and Leisure and the Heritage Lottery Fund - would increase the museum space by 1,225m 2.The museum authorities are keen to maximise the presence of the building in its botanical garden location, and improve facilities to increase visitor numbers.
But opposition to this planned work, which would include moving the entrance and altering the extension's celebrated canopy, is gathering momentum.
Protest has come in the form of letters and a campaign from the Ulster Architecture Heritage Society. Other groups involved include Docomomo's UK contingent.
Unusually, opposition has also come from the Arts Council of Northern Ireland (ACNI), which normally refuses to comment on planning applications. In a letter of objection to the planning service, the ACNI said: 'We are very concerned about the proposed treatment of the entrance facade, which would place new entrance doors in the centre of the elevation and introduce a glass wall underneath the existing entrance canopy, behind which a new café is to be located.
'This presents some confusion in reading the building, and also goes some way to disrupting the character and aesthetic of the facade, which is remarkably sculptural and inventive.'
The facade has been described by architecture historian Robert Hughes as '[having] the geological grain of a quarry face, hewn and sculpted'.
The ACNI also helped to fund a book, Modern Ulster Architecture, which highlights the museum as being of 'major architectural importance'.
'We would echo these views, ' the ACNI letter goes on, 'and ask that the planning service takes them into consideration when reviewing the plans, thereby ensuring the architectural quality of this landmark is not compromised during redevelopment.'