Secretary Ed Miliband has insisted the government's willingness to consider formally apologising for the the UK's role in the transatlantic slave trade will not lead to higher costs for the British taxpayer.

The prime minister has said the UK will not pay reparations to affected countries, but declined to say whether his new approach could involve additional taxpayer money.

Speaking on the BBC's Newscast podcast, Miliband said previous British governments had a "sweep it under the carpet" attitude to the pain and consequences of slavery, citing what he described as former Prime Minister Sir Tony Blair's "sorry not sorry" remarks on the issue nearly two decades ago.

In 2007, Sir Tony said the UK's involvement in the slave trade was a matter of "deep sorrow and regret".

"Tony Blair did sort of do a kind of sorry not sorry situation. He kind of expressed sorrow, and then said sorry, and then it was walked back by number 10," Miliband said.

Miliband said the former prime minister's approach was still referred to and came up in a recent conversation between Andy Burnham and the Prime Minister of Barbados Mia Mottley.

In addition, Miliband claimed, he and Burnham inherited a more recent mess, which is how the last Commonwealth Heads of Government Meeting (CHOGM) played out in Samoa two years ago.

Miliband said: "On the second day as my time as foreign secretary, I was told, 'look, one of your tasks is CHOGM 2024, which happened in Samoa, didn't go well.' To use sort of diplomatic speak, it ended up in a sort of punch up, a sort of verbal punch up about this whole issue."

He added: "This has really been hanging around as an issue for the Commonwealth for sort of 20 years, really. But it's grown and grown." Given that, Miliband said, "we thought it was right to confront this issue and not to just try and sort of pretend that it didn't exist". Burnham now says the government is open to formally apologising for slavery.

Ministers are beginning what they call a "structured dialogue" with affected countries, with the expectation that the apology may come at around the time the prime minister hosts the G20 Summit of world leaders in Manchester in November 2027. "Is it weak to do this?

I think it's the opposite of weak. I think fragile weak countries can't face up to their past. I'm really proud of Britain, but being proud of your country is also being willing to face up to things you didn't do, right?" Miliband said. He said he had asked to be provided with a historical digest of the UK's involvement in the slave trade.

"Over three million people shipped, really with the British state's complicity, over a long period of time, couple of centuries actually, hundreds of thousands of them didn't make it and died," the foreign secretary said.

"Those who did make it had appalling conditions. Reading about the conditions on the ships and what happened to them when they arrived in the Caribbean and the Americas is really pretty harrowing." Now he and the prime minister begin a process likely to formally apologise for this -and, they hope, create space for the Commonwealth to turn its attention to other things.