The liberal party D66 and the Christian Democrats (CDA) should work together to determine which potential coalitions can count on a majority in both the lower and upper houses of parliament, Wouter Koolmees, who has been charged with making an initial assessment of cabinet options, told reporters on Tuesday evening.

His report marks the end of the first stage in the process of forming a new coalition government in the Netherlands, following last month’s general election.

Party leaders Rob Jetten (D66) and Henri Bontenbal (CDA) will work together for the next three weeks to see if agreement can be reached with other parties on themes such as migration, housing, defence, nitrogen-based pollution, the economy and the Dutch investment climate, Koolmees said. It should be a “positive agenda,” he said.

“These parties have not thrown up any obstacles to other parties, and the other parties have not objected to them,” Koolmees told reporters. D66 won 26 seats in last month’s general election and the CDA won 18.

VVD leader Dilan Yesilgöz, whose party won 22 seats in the 150-seat lower house of parliament, has repeatedly said her party will not work together with the left-wing green alliance GroenLinks-PvdA, which has made a centre-left coalition impossible. Her preferred option would mean involving the far-right JA21.

GroenLinks-PvdA, JA21 and small Christian party ChristenUnie would be potential coalition partners, Koolmees said, but the CU has ruled itself out.

A majority in the upper house of parliament, to ensure that legislation passes in both chambers, is also important to take into account, Koolmees said.

The right-wing coalition favoured by Yesilgöz can only count on 24 seats in the 75-seat senate, while a centre-left coalition would have 35.

“Compromises will have to be made,” Koolmees said. “We are talking about long-term planning.”

The parties, he added, “carry a responsibility for the interests of the Netherlands as a whole, and that means working together in The Hague, and outside with unions, employers and industry.”