Conservative MPs have reacted angrily to an intervention by Joe Biden, the US Democratic presidential candidate, in the UK Brexit talks, accusing him of ignorance of the Northern Ireland peace process.In a tweet on Wednesday, Biden warned the UK there would be no US-UK free trade agreement if the Brexit talks ended with the Good Friday agreement being undermined. He tweeted: “We can’t allow the Good Friday agreement that brought peace to Northern Ireland to become a casualty of Brexit.“Any trade deal between the US and UK must be contingent upon respect for the agreement and preventing the return of a hard border. Period.”His intervention was welcomed by Richard Neal, the chairman of Congress’s ways and means committee.The backlash was led by the former cabinet minister Iain Duncan Smith, who told the Times: “We don’t need lectures on the Northern Ireland peace deal from Mr Biden. If I were him I would worry more about the need for a peace deal in the US to stop the killing and rioting before lecturing other sovereign nations.”Donald Trump has made law and order a key theme of his re-election campaign after months of unrest triggered by the death of George Floyd in Minneapolis in May.David Davis, the former Brexit secretary, said: “Perhaps Mr Biden should talk to the EU since the only threat of an invisible border in Ireland would be if they insisted on levying tariffs.”Biden spoke out after the UK foreign secretary, Dominic Raab, met the House Speaker, Nancy Pelosi, in Washington in a bid to reassure her that the British government was not seeking a hard border on the island of Ireland via measures in its internal market bill, a move that is seen by the US pro-Irish lobby as potentially fatal to the peace process.Q&AWhat is the UK internal market bill?ShowThe internal market bill aims to enforce compatible rules and regulations regarding trade in England, Scotland, Wales and Northern Ireland.Some rules, for example around food safety or air quality, which were formerly set by EU agreements, will now be controlled by the devolved administrations or Westminster. The internal market bill insists that devolved administrations have to accept goods and services from all the nations of the UK – even if their standards differ locally.This, says the government, is in part to ensure international traders have access to the UK as a whole, confident that standards and rules are consistent.The Scottish government has criticised it as a Westminster “power grab”, and the Welsh government has expressed fears it will lead to a race to the bottom. If one of the countries that makes up the UK lowers their standards, over the importation of chlorinated chicken, for example, the other three nations will have to accept chlorinated chicken too.It has become even more controversial because one of its main aims is to empower ministers to pass regulations even if they are contrary to the withdrawal agreement reached with the EU under the Northern Ireland protocol.The text does not disguise its intention, stating that powers contained in the bill “have effect notwithstanding any relevant international or domestic law with which they may be incompatible or inconsistent”.Martin Belam and Owen BowcottRaab has argued that the measures in the UK internal market bill are proportionate, precautionary and necessary due to the EU’s politicising of the stuttering talks on a trade deal between the UK and the EU.However, the EU hit back on Thursday, saying an agreement on a trade and security deal remained conditional on the government pulling the contentious clauses in the internal market bill.The European commission’s vice-president for the economy, Valdis Dombrovskis, said: “If the UK does not comply with the exit agreement, there will no longer be a basis for a free trade agreement between the EU and the UK. The UK government must correct this before we continue to negotiate our political and economic relations.”The dispute between Biden and Downing Street poses a broader threat to UK interests if Biden, a pro-EU and pro-Ireland politician, decides to turn against Boris Johnson, who has made a virtue of his close relations with the Trump administration.The former UK trade minister Conor Burns tweeted: “Hey JoeBiden would you like to discuss the Good Friday agreement? It is also called the Belfast agreement so it doesn’t offend both traditions. Did you actually know that? I was born in NI and I’m a Catholic and a Unionist. Here if you need help.”The Conservative MP for Beaconsfield, Joy Morrissey, replied that “Biden is shamelessly pandering to the American Irish vote while refusing to engage with the UK government or UK diplomatic channels. Nice.”She later deleted her tweet, but added: “Clearly it’s all about the Irish American vote.”Burns added: “The error those of us who supported Brexit was to assume the EU would behave rationally in seeking a free trade agreement with a large trading partner like the UK..”Alexander Stafford, the Conservative MP for Rother Valley, tweeted: “Is this the same JoeBiden who once described Britain’s position in Northern Ireland as ‘absolutely outrageous’. And who hit the headlines in the 1980s for his stand against the deportation of IRA suspects from the US to Britain?”John Redwood, a leading Brexiter, said: “Trade deals are nice to have but not essential. We did not have a trade deal with the US when we were in the EU. Getting back full control of our laws, our money and our borders is essential.”Theresa May’s former chief of staff Nick Timothy rejected the frenzy, dismissing “the sudden discovery that Democrats don’t like Brexit and prefer the Irish”.Other Tory MPs including Stewart Jackson tweeted articles claiming that two of the representatives criticising the UK over the Good Friday agreement were overt IRA sympathisers, and a third was a supporter of Martin McGuinness, the now deceased former deputy first minister for Northern Ireland.The shadow foreign secretary, Lisa Nandy, said: “This shows the scale of the damage the government have done to Britain’s standing in the world. They’ve lost trust and undermined cooperation at the moment we most need it – and all to tear up an agreement they negotiated. Reckless, incompetent and utterly self-defeating.”Daniel Mulhall, the Irish ambassador to the US, has been working the corridors in Washington for the past fortnight, lobbying to lessen the threat the Irish perceive to the Good Friday agreement posed by the British proposals. He has been tweeting his gratitude to those representatives issuing support for the Good Friday agreement.No free trade deal between the UK and the US can be agreed unless it is supported by two-thirds of Congress.In a sign of Trump administration concern about the row, Mick Mulvaney, Trump’s former acting chief of staff, will shortly make his first trip to the the UK in his new role as the US special envoy for Northern Ireland.The Foreign Office, criticised by some for failing to anticipate the likely US backlash, will argue Raab’s visit to Washington may have drawn a predictable reaction from some corners, but was necessary to reassure and counter Irish propaganda.But UK diplomats will be anxious that the UK is not seen to adopt a partisan stance in the US elections, especially since Biden currently holds a fragile poll lead. More