A decade-long planning battle stemming from a “mistake” by the Planning Authority will culminate on Thursday when an appeals tribunal holds its final hearing on a five-storey apartment block in a villa area of Balzan.

Residents are appealing a permit for the flats on the corner of Triq San Franġisk and Triq San Gabriel, which, they say, are totally out of proportion with the surrounding two-storey villas and incompatible with the local context.

Moreover, the residents claim that since the permit was issued in 2012, the developer went on to illegally add a penthouse, which was specifically prohibited by the permit conditions.

The issue is attributed to a mistake when an application was first submitted in 2004, with the area wrongly zoned as a terraced house area instead of a villa area.

The mistake, investigated and confirmed by the Planning Authority’s audit office and the Ombudsman, was caused by the “misinterpretation” of central local plans due to faded watercolours on the temporary provision schemes in which the area was labelled as a villa area.

The Ombudsman at the time advised the then Malta Environment and Planning Authority that neighbours should not suffer for its mistakes while the developer reaped the rewards.

More than 400 residents signed a petition backed by the local council calling for the mistake to be corrected.

The Planning Authority’s board overwhelmingly rejected the project in 2009, ruling it was not compatible with the existing villas, and began the process of rezoning the area.

But the developer appealed the refusal and obtained an injunction against the rezoning. The Planning Review Tribunal upheld the appeal in 2012, granting a permit for the apartments.

The planning watchdog then took the matter to court, but in a controversial move that angered residents, the authority later announced it had reached an out-of-court settlement with the developer and had withdrawn its objection to building apartments in the area.

The developer later obtained a further permit for minor amendments and started works on the project, which has now largely been completed.

The residents, whose appeal against the development is now under consideration, contend a penthouse is illegal because it was specifically prohibited in the conditions of the permit.

The review tribunal will hold its final hearing on the latest appeal tomorrow and will announce its decision in the coming weeks.