National leader Judith Collins says she deliberately refused to receive details of now ex-Minister Iain Lees-Galloway's affair after she received a tip-off about his behaviour yesterday.

Instead, she said she took the information directly to Prime Minister Jacinda Ardern, who thanked her for passing it on.

Collins has also pushed back on any suggestion that she was playing politics over the saga – "that is complete rubbish".

This comes after Ardern this morning sacked Lees-Galloway over an inappropriate relationship he had with a staff member in one of the departments he headed.

The relationship lasted 12 months and has cost Lees-Galloway his political career - he will not contest September's election.

Ardern said it was "untenable" for him to continue as a Minister – he was the Minister of Work Place Relations, as well as ACC and Immigration.

The Prime Minister's surprise press conference followed Collins telling media this morning that she had received a "tip off" about a Labour Minister that she had passed on to Ardern.

She would not elaborate on this when speaking to media this morning.

But after Ardern's announcement, Collins elaborated about her involvement this afternoon.

"I alerted the Prime Minister to the information an hour after I received it," she told media before going into the House this afternoon.

"I refused to receive any details from the informant, and I asked the information [to be] sent directly to the Prime Minister's Chief-Of-Staff."

Collins said she spoke to Ardern after question time yesterday afternoon, at around 3 pm.

She said she was "not at all" playing politics with the information when she was speaking to media this morning.

"It was a straight question, I gave … a straight answer," she said.

Collins was asked by a MediaWorks host if she had "received anything about Labour ministers or Labour MPs".

Collins said: "I have actually" before saying she had passed the information on to Ardern.

Lees-Galloway's resignation comes just a day after now National ex-National MP Andrew Falloon was forced to resign in disgrace after it was revealed he had sent inappropriate material – including pornography – to at least four young women.

In that situation, information about Falloon's behaviour was passed on to the Prime Minister's office, which then passed it on to National.

But this afternoon, Collins suggested Ardern did not move fast enough to bring the issues to her attention.

Collins said it took the Prime Minister two days to inform her office of information that she needed to know about Falloon – "I've taken just over an hour to let her know [about Lees-Galloway]."

Meanwhile, Collins said things need to change when it comes to the culture of Parliament and has written to Ardern to say as much.

"I have said as the leaders of the two major parties in Parliament that we should … sit down and work out what we believe MPs, and also staff, should have a safe work environment."

She said Parliament is not always a safe working place – "that is not okay and I believe that she and I have an opportunity to fix it".