Britain will "not be aligning with EU rules" in any post-Brexit trade deal, the foreign secretary has said.
Dominic Raab argued agreeing to stick strongly with EU regulations would "defeat the point of Brexit".
But Irish PM Leo Varadkar said the UK needed to commit to a level playing field to get a free trade deal.
Talks to negotiate a free trade deal between the UK and the EU are due to start next month, following the UK's formal withdrawal from the bloc.
On Monday Boris Johnson is expected to set out his position ahead of those talks, where he will tell the EU he is prepared to accept customs checks at Britain's borders if he cannot secure the sort of trade deal he wants.
EU chief negotiator Michel Barnier will also outline his approach to negotiations.
One option the PM could support would be a Canada-style free trade deal which allows tariff-free trade for the majority of goods, but would not cover the UK's service industry - which accounts for more than 80% of UK jobs.
Reports in recent days have suggested EU chiefs want the UK to continue to follow EU rules on standards and state subsidies - while accepting the jurisdiction of the European Court of Justice in any trade disputes.
The PM is expected to say that he will accept no alignment and no jurisdiction of the European courts when talks start in March.
He is also preparing to say he would rule out relaxing rules on workers' rights, food hygiene standards and environmental protections.
'Rigid red lines'
Speaking to the BBC's Andrew Marr Show, Mr Varadkar said it was possible for the UK to have a "Canada-style agreement".
However, he added: "Canada isn't the UK; you're geographically part of the European continent, we share seas and airspace and our economies are very integrated.
"And one thing we feel very strongly in the EU is that if we are going to have tariff-free, quota-free trade with the UK, which is essentially what we have with Canada on almost everything, then that needs to come with a level playing field.
"We, for example would have very strong views on fair competition and state aid."
A level playing field is a trade policy phrase for a set of common rules and standards that prevent businesses in one country undercutting their rivals over those operating in other countries in areas such as workers' rights and environmental protections.
He also cautioned against "setting rigid red lines" for the post-Brexit trade negotiations arguing "it makes coming to an agreement more difficult because the other side doesn't feel like it has got a fair deal unless those red lines are turned pink."
Mr Raab said the UK would enter trade talks "with a spirit of goodwill" but added "the legislative alignment - it just ain't happening".
Labour's John McDonnell said Mr Johnson's desire to diverge from EU rules "contradict" what the PM had previously said on protecting environmental, consumer and employment rights.
"On the one hand he said there will be [protections] on the other hand he is sabre-rattling saying that won't happen in the negotiations," he said.
But Brexit Party leader Nigel Farage welcomed the prime minister's approach arguing it was in the UK's "national interest" to be "a competitor on their [the EU's] doorstep."
The government also wants to make progress in striking free trade agreements with countries such as the United States, Japan, Australia and New Zealand.
The EU's own approach to the negotiations needs to be agreed by all 27 member states - which would be unlikely to happen before the end of February.
While the UK officially left the EU at 23:00 GMT on Friday, it will remain wedded to EU rules during a transition period which ends in December this year.
The UK can request an extension to this transition period, but Mr Johnson has previously said he will not do so.