Grant Robertson says he sought assurances from the Labour Party after concerns were raised with him

But the Finance Minister won't say whether those were sexual assault allegations against a staffer.

National's deputy leader Paula Bennett claims Robertson - and three of the Prime Minister's senior staff - had known about those for some time.

Robertson says he checked that issues were dealt with appropriately - but won't confirm or deny Bennett's claims.

He says very serious allegations have been raised and need to be worked through.

Robertson says this is not a political game of who knew what, when - it's about young people.