A “wounded” Theresa May must give up her pursuit of a hard Brexit or face the prospect of Holyrood holding back legislation to progress Britain’s divorce from the European Union, Ian Blackford has suggested.

Speaking as the Prime Minister today publishes her flagship Repeal Bill, the SNP leader at Westminster stressed his party was seeking to compromise and co-operate with the Conservative Government for the benefit of Scotland and the rest of the UK and urged her to listen to “reasoned voices”.

In an exclusive interview with The Herald, he said: “We’re extending that hand and saying we are willing to work with you but I don’t get the impression at the moment, even though the Government is talking about a Legislative Consent Motion[LCM], that they have adopted the right manner in terms of wanting to negotiate.”

Claiming that the Tory Government was not showing the devolved administrations due respect and was paying “lip-service” to consulting with them, Mr Blackford said: “Theresa May has to take a step back; she is a wounded prime minister…We’re talking about a minority administration that does not have the authority that she sought from the people in the UK.

“Our objective…is to make sure we can be represented at the table in those negotiations. We can only do that if we have a meaningful debate with the UK Government. That has not yet happened; the clock is ticking.”

Asked if it was possible Holyrood could withhold consent for an LCM – the means by which it agrees to Westminster legislating on devolved matters – and thereby exert some leverage on Mrs May, the Nationalist leader said: “If at the end of the day we have an intransigent government that will not listen to reasoned voices - and I may say so a[Scottish] government that has a mandate from the people of Scotland - then, of course, we will need to look at the options that we have. And consent on an LCM is part of that. But I don’t want to be in a position where we are threatening anybody; we’re trying to achieve consensus because that’s the right thing to do.”

His remarks follow those of Michael Russell, the Scottish Government’s Brexit minister, who made clear Holyrood’s consent to granting an LCM was “not a given”.

Asked what would happen if the PM continued to pursue her current path, Mr Blackford replied: “Of course, there’s an issue for us and how we respond to that but she will find Parliament in London will also want to have a say in these matters and she will get into very choppy waters if she chooses not to want to listen to a broader array of opinion on the matter.”

His comments came as the National Audit Office, the spending watchdog, in a damning report hit out at the UK Government’s failure to prepare a new customs system in time for Brexit, warning of a "horror show" if officials were forced to process imports and exports manually.

At Westminster, David Davis, the Brexit secretary, said the Repeal Bill, which abolishes the 1972 Act that took Britain into the EU and transposes all EU law into UK law, was one of the most significant pieces of legislation ever to pass through Westminster.

“This bill means we will be able to exit the European Union with maximum certainty, continuity and control. That is what the British people voted for and it is exactly what we will do; ensure that the decisions that affect our lives are taken here in the UK,” insisted Mr Davis.

In Brussels today, Jeremy Corbyn, the Labour leader, Nicola Sturgeon and her Welsh counterpart Carwyn Jones will all hold talks with Michel Barnier, the EU’s chief negotiator, who is preparing for the second round of Brexit talks on Monday.

He stressed that while he wanted to listen to the different points of view in the British debate, he would “only negotiate with the UK Government".

Mr Corbyn claimed his “extended meeting” with the EU's chief negotiator showed Labour’s “growing importance” to the Brexit process. He declared: “Labour is a government-in-waiting and we are ready to take up the responsibility for Brexit negotiations.”

At Holyrood, the FM’s spokesman said her meeting with Mr Barnier was “not about holding separate Scottish negotiations” as she accepted the EU would only deal with the UK.

He said: “This is an opportunity to brief Mr Barnier on Scotland's priorities and seek to enhance our understanding of current EU position as Brexit negotiations continue.

“Our priority is protecting Scotland’s vital interests, and building consensus against an extreme Brexit outside the single market, which would be potentially disastrous for jobs, investment and living standards.”

Lewis Macdonald, Scottish Labour’s Europe spokesman, said: “Unlike the Tories, Labour wants a jobs-first Brexit that will prioritise the economy, jobs and living standards.”

For the Liberal Democrats, Alistair Carmichael, the former Scottish Secretary, urged Ms Sturgeon to remember she was in Brussels to represent all of Scotland.

“Rather than use this trip to bang on about independence, she should recognise that the best way to keep Scotland in the EU is to keep the whole of the UK in the EU.”

The comments came as credit ratings agency Moody's warned the UK's creditworthiness was under pressure due to uncertainty over the result of Brexit negotiations and that Britain would face materially weaker growth if it failed to secure a good deal on trade.