The UK government’s internal market bill is “an abomination which would cripple devolution”, Nicola Sturgeon has said, escalating already fierce criticism of the proposals from across the devolved administrations. Earlier the Welsh government described Westminster’s plans for a post-Brexit UK-wide internal market as “an attack on democracy and an affront to the people of Wales, Scotland and Northern Ireland”. The Plaid Cymru leader, Adam Price, said the bill signified “the destruction of two decades of devolution”, while Scottish Labour’s Alex Rowley described it as “a farce that threatens the very foundations of the United Kingdom”. Later in the day David Melding quit the Tory frontbench in the Senedd over the proposals and launched a withering attack on Boris Johnson. Stepping down as shadow counsel general, Melding said: “The publication of the internal market bill had done nothing to lessen my anxieties about the dangers facing our 313-year-old union and indeed they have been gravely aggravated by the decisions made in the last few days by the prime minister. “I feel it is necessary to speak out against what I consider to be a lack of statecraft at this crucial time for the UK’s very survival as a multi-national state.” The internal market bill, which sets out trading arrangements across the UK after the transition period, also includes clauses which negate key aspects of the EU withdrawal agreement – and which the UK government on Tuesday conceded breaks international law. In a strongly worded statement following the publication of the draft bill at lunchtime, Sturgeon said: “The UK government are not only set to break international law – it is clear they are now set to break devolution.” Sturgeon pledged that her government would “fight tooth and nail” against proposals that include a mutual recognition regime, requiring regulatory standards in one part of the UK to be automatically accepted in others, and which she argued would mean “a race to the bottom when it comes to things like food standards and environmental protections”. She said plans would prevent the Holyrood parliament from effectively legislating in a whole range of areas and could, for example, lead to Scotland being forced to accept chlorinated chicken. Jeremy Miles, the Welsh counsel general and minister for European transition, told the Guardian the bill in its current form had “no prospect” of getting Senedd consent. “The question is if they don’t get that consent whether they will proceed regardless”, he said. Describing the proposals as “an outrageous power grab”, he reiterated that the “cavalier” bill “seriously imperils the devolution settlement”. In an indication of how the devolved administrations are cohering in opposition to the plans, Nichola Mallon, the SDLP deputy and minister for infrastructure, tweeted that she was “extremely concerned at the actions of the British government” and had discussed attempts to undermine devolved power on infrastructure with Scottish government counterpart Michael Matheson. The Welsh government also accused Westminster of failing to consult them adequately. Miles said: “We didn’t have access to the bill until late last night. Whatever your view about the merits of it, if you’re going to put forward a bill which cuts into devolution then plainly anything that is encroaching on devolved territory needs to be discussed and agreed. That has absolutely not happened”. There are also profound concerns about a proposed oversight body that would hold any new devolved bills to a “market impact test”, which the Scottish government believes would have jeopardised Scotland-only initiatives such as free university tuition. Sturgeon said: “Under this bill, the Scottish parliament would not have been able to pass its world-leading legislation on minimum unit pricing of alcohol – a fact which will deeply concern the broad coalition of Scottish civic society which backed this vital public health measure.” The Welsh and Scottish governments wrote to Michael Gove setting out their concerns in July, when the proposals first emerged, warning they would put Scotland and Wales on a collision course with Westminster. Sources at the time reported a more aggressive approach towards devolution from a new generation of Conservative politicians. But Downing Street denied the bill was a “power grab”, insisting there would be no change to the powers already held by the devolved administrations and highlighting that additional powers would be returned post-Brexit in “at least 70” policy areas. Speaking after prime minister’s questions, Johnson’s spokesman said: “What the devolved administrations will enjoy is a power surge when the transition period ends in December. “There will be no change to the powers that the devolved administrations already have and the vast majority of powers with devolved competencies returning from Brussels will go straight to Holyrood, Stormont and Cardiff Bay.”