One of the UK’s most respected diplomats has accused Boris Johnson of planning three separate breaches of international law, warning that trust in the UK abroad is being shredded.

Kim Darroch, a former national security adviser and US ambassador, has attacked plans to neuter commitments to the European Convention on Human Rights (ECHR), arguing they will violate the Good Friday Agreement.

In an interview with The Independent, he said the threat sits alongside moves to tear up the Brexit deal for Northern Ireland and to deport refugees to Rwanda, breaking the Geneva Convention.

“I think you can argue that this government is breaching international law in three areas,” Lord Darroch argued.

Seizing on Dominic Raab’s plans to allow the UK to ignore ECHR rulings, the crossbench peer warned: “The ECHR is enshrined in the Good Friday Agreement as a guarantee of the rights of all individuals in Northern Ireland.

“Now they want to effectively disapply, by domestic law, some parts of the ECHR, and that looks to me to be in danger of breaching our commitments in the Good Friday Agreement”.

Pointing to the damage to the UK’s reputation abroad, Lord Darroch added: “Everything I pick up from people in the Brussels institutions is that trust in the British government has broken down.”

In the interview, the chair of the internationalist campaign group Best for Britain also argued that voters would welcome Mr Johnson sitting down with the EU to strike a better Brexit deal to ease severe economic damage to the UK.

He ruled out an early return to the single market or customs union – despite the benefits that would bring – “certainly not in this parliament and perhaps not in the next one either”.

However, calling for side deals to soften the pain for exporters, scientists shut out of the Horizon project and the City of London, Lord Darroch said: “I think people would see agreements of this kind as common sense.”

The peer, who is also a former UK ambassador to the EU, argued that most voters never backed “the hardest of Brexits that satisfies a section of the Conservative Party”.

And he suggested that the prime minister might be willing to compromise but for the crisis surrounding him – turbocharged by two devastating by-election defeats last week.

“It’s just hard to know what he really, personally believes. It’s a bit of a mystery to me,” Lord Darroch said.

“I don’t rule out him doing deals, but at the moment he feels his position as prime minister is sufficiently under threat that he needs all the support he can find.”

On the pressure not to soften the Brexit terms, the peer pointed out: “Brexiteers are walking around now looking pretty gloomy about the way it’s panned out. Wouldn’t it help them to make it less damaging?”

Lord Darroch also chided Sir Keir Starmer, saying: “I think Labour could be a bit braver and make the case more publicly for a different, better form of Brexit.

“As the impact of Brexit becomes more apparent, I wonder if they might be forced to take more of a position – because we are in for a really bad time on inflation, a recession maybe. It’s looking very bleak.”

The bill to override the Northern Ireland protocol, which Mr Johnson hailed as “fantastic” when he signed it in 2019, cleared its first Commons hurdle on Monday.

The government admits it breaks the Brexit withdrawal agreement, but argues that the “doctrine of necessity” trumps that because of Unionist opposition to the Irish Sea trade border the Protocol created.

Lord Darroch said: “On the Northern Ireland protocol, you just cannot unilaterally disapply and revise and rewrite parts of an international agreement through domestic legislation.”

The United Nations high commissioner for refugees has attacked the Rwanda deportations, pointing to the UK’s commitment in the 1951 Refugee Convention to take responsibility for asylum seekers.

Lord Darroch said: “We have international commitments on the treatment of refugees through the Geneva Convention. I just don’t think what we are doing with Rwanda is compatible with that.”

The Good Friday Agreement, the landmark 1998 deal that ended the Troubles, is an international agreement between the British and Irish governments.