Labour MPs are not looking to raise taxes to fund more benefits, the cabinet minister Nick Thomas-Symonds has said.

In messages between the work and pensions secretary, Pat McFadden, and Peter Mandelson released on Monday, McFadden wrote: “Every meeting I have is: ‘Who can we tax in order to pay benefits to others?’ They’re asking the wrong questions.”

The private WhatsApps were shared as part of a tranche of data that MPs voted to release in February relating to Mandelson’s appointment as US ambassador – from which he was subsequently sacked – including texts with ministers and senior officials.

Thomas-Symonds said the messages were “embarrassing” but were in the public domain because of the government’s commitment to comply with the humble address motion passed by parliament.

He also confirmed that he had not released his own messages because his phone had been stolen, but said he had verbally described his messages with Mandelson to the Cabinet Office.

Asked about McFadden’s comments, he said it was not his experience that Labour MPs were demanding tax rises to pay for benefits, and said McFadden was committed to helping to find people more opportunities for work rather than a life on welfare.

“Look, they are embarrassing. I’m not hiding from that, but the reason they’re in the public domain is because of the government’s desire to comply with the humble address,” he said.

“[McFadden’s] view has always been about an emphasis not on the benefits side, but an emphasis on giving people opportunities, and that’s why you’ve seen over the last week,” he added, referring to the recent report by the former health secretary Alan Milburn on tackling youth unemployment.

Asked about the culture in the parliamentary party of demanding more spending on benefits, Thomas-Symonds said it was “not my experience, obviously Pat is talking there about meetings he’s been in. It’s not my experience.”

He added: “I don’t accept that Labour MPs, all of us together, are not determined to tackle the scourge of youth unemployment … in that work we are absolutely united as a parliamentary party.”

He said that the welfare bill was also rising because of the increase in the state pension and the government’s commitment to the triple lock. “I am proud that we are doing that, looking after pensioners up and down the country,” Thomas-Symonds said.

The cabinet minister said he was not surprised to see so many congratulatory messages to Mandelson – who was sacked after revelations about his closeness with the late child sex offender Jeffery Epstein. He said he had been unaware about the extent of their friendship until files had been released by the US Department of Justice last year.

“I had no idea about the depth and the darkness of the relationship between Peter Mandelson and Jeffrey Epstein,” he said. “I was shocked, absolutely shocked, last September when that came to light.”

Thomas-Symonds said there were messages on his stolen phone congratulating Mandelson on his appointment. “I lost significant amounts of data, not just WhatsApp, but personal photographs as well. This was my personal phone,” he said, adding there were messages “congratulations about my appointment, [Mandelson’s] subsequent appointment. There would have been an exchange when he was campaigning to be the chancellor of the University of Oxford. So I’ve always been someone in favour of transparency.”