Housing corporations which merge in an effort to become more efficient end up, on average, with higher operating costs than those which remain independent, according to new research out on Friday.

The environmental assessment agency PBL says its findings should make housing corporation bosses more wary about justifying mergers in financial terms.

The extra spending is due to company culture and the way the organisation has been set up rather than the merger itself, the PBL said.

Since 1997, the number of housing corporations in the Netherlands has fallen from 764 to around 380.