The Labour party will attempt to draw a line under divisions over its decision to support the triggering of article 50, promising that it will refuse to back any Brexit deal that does not deliver “the exact same benefits” as the UK enjoys as a full member of the European Union.

In a wide-ranging speech on Monday, Labour’s Brexit spokesman Keir Starmer will warn that the Brexit process is in danger of being hijacked by Tory hardliners who sense a “once in a generation chance” for Britain to extricate itself from employment rights, environmental protections and investment in public services.

His words will echo those of Labour leader Jeremy Corbyn, who on Sunday said his party would oppose plans to hand ministers “Henry VIII” powers to change European Union laws as they are returned to Britain without full parliamentary scrutiny.

In a major policy speech at Chatham House, Starmer will harden Labour’s Brexit stance, warning that there is a “worrying and increasingly powerful move on the government benches to sever our links with Europe”.

“This is the authentic voice of the Brexiteers. Those who have argued for decades that exiting the EU offers a once-in-a-generation chance for Britain to extricate herself from the entire European social and economic model,” he will say. “Once a small minority in the Conservative party, the Brexiteers are now in office and in power. This ideologically driven approach to Brexit would be disastrous and divisive.”

Starmer will add that exiting the EU must not be used as a pretext for rolling back “hard-fought protections” such as paternity leave, holiday pay and equal rights for part-time and agency workers.

Just 48 hours before Theresa May is set to formally trigger article 50 – the formal process for exiting the EU – Starmer will set out six tests which any deal must pass, or face the opposition of Labour in the House of Commons.

In January, Brexit secretary David Davis said a new “comprehensive free trade agreement and a comprehensive customs agreement” would deliver “the exact same benefits as we have [now]”. Starmer will argue that this “exacting standard” is of the government’s own making. “Failure to deliver this deal will lie squarely at the government’s door,” he will say.

Speaking to the Guardian ahead of the speech, he said: “All these tests are tests that at one stage or the other the government has said it is prepared to meet, and therefore it’s impossible for them that they cannot be met, including the single market test – those are David Davis’ words. They are tough tests, but we are talking about the future of the UK in the EU and the world.”

He will insist that Theresa May – whom he will accuse of being “guarded, closed, unable to build a consensus or form alliances” – must abandon the suggestion that “no deal is better than a bad deal”, and agree transitional arrangements to prevent Britain being hit with high tariffs if it experiences a “cliff-edge” fall out of the EU.

He will also insist on May’s commitment to maintaining equal cross-border security and policing, calling for clarification on whether Britain will be a member of Europol and retain the European arrest warrant.

Potentially putting himself at odds with some in the party, he will stress the need for “fair and effective management of migration” and call for “a new approach to immigration that has the consent of the British people and is managed in their interests”, with costs and benefits more transparently distributed.

“Freedom of movement is an EU rule, therefore when we leave, those rules fall away and we have to decide what immigration rules and policy go in its place,” he told the Guardian. “What I’m arguing for in the speech is new rules that reflect both economic demands and those of the community.”

Starmer will argue that the vote for Brexit, as well as reflecting concerns about the EU and its reform, was a reflection of voters’ belief that “politics and the economy no longer work for them or their communities”, adding that they were offered “false hope” that leaving the EU would change that.

“But the truth is that Brexit cannot tackle stagnant wages, resolve a chronic skills gap, reduce unequal growth across the UK or improve underfunded public services,” he will say. “Brexit cannot mend public trust in politics or build more cohesive communities. And it cannot provide a place for Britain in a more complex and chaotic global order.”