The government’s leader in the Senate, George Brandis, has described the Queensland Liberal National Party opposition as “very, very mediocre” and warned One Nation is likely to win “quite a few” seats at the state election.

In another gaffe by the accident-prone Brandis, he also suggested the merger between the Liberals and Nationals in Queensland might be revisited. The frank remarks were made when Brandis didn’t realise the mic was on at a Victorian Liberal function he attended at the weekend. He gave his blunt assessment of the situation in his home state to Victorian Liberal Party president Michael Kroger.

The prospect of One Nation doing well at the Queensland election, due in 2018, is being much talked about after Pauline Hanson’s party achieved four senators at the double dissolution, giving it a strong platform.

The former Liberal premier of Queensland, Campbell Newman, has predicted that whichever party forms the state government next term will need to rely on One Nation. He forecasts One Nation will win between six and 11 state seats and says that present polling is underestimating its real support.

One Nation has taken particular heart for its future prospects after the Trump victory, which Hanson celebrated with champagne. Like Trump, One Nation harvested votes from those who feel victims of economic change.

Kroger asked Brandis how things were in Queensland and how Opposition Leader Tim Nicholls was going.

“Well, they’re not very good,” Brandis replied. “I’d say that the state opposition is very, very mediocre and the state government is very, very mediocre.

"The thing that is alarming everyone, as you’d expect, [is] the sudden spike in One Nation which is now at about 16% and … their strength is in heartland National Party seats and heartland Labor Party seats, the old industrial seats around Ipswich and Brisbane.

"So I think there is every reason to believe that they will win quite a few seats in the state election.”

Brandis said the Queensland Labor government’s move to bring back compulsory preferential voting in its changes to the electoral system “somewhat attacks the raison d'etre of the merger of the Liberal Party and National Party”.

When Kroger agreed, Brandis went on to say: “I think there might be a revisiting of things as a result of compulsory preferential”.

Brandis was a critic of the plan to merge the Liberal and National parties, which took place in 2008.

In the 1998 Queensland election One Nation won 11 seats with 22.7% of the vote.

The latest faux pas by Brandis follows his clash with the former solicitor-general, Justin Gleeson, who quit over Brandis issuing a direction that all requests for Gleeson’s advice had to go through his office. Brandis later withdrew the order just as the Senate was set to overturn it.