Boris Johnson has said he is anxious MPs in Parliament may "undermine" the UK's ability to strike a Brexit deal with the EU, claiming there is now "movement" in his negotiations.
He told ITV News Political Correspondent Libby Wiener: "My anxiety is that stuff going on in Parliament can actually undermine the UK's negotiating position."
"There is movement under the keel," he said, adding: "It's therefore vital that our EU friends don't constantly think at the back of their minds, hmm, this thing could be blocked in Parliament, Brexit could be thwarted."
Prime Minister Boris Johnson said: "What I want to do now, which is I think what most people in this country want the Government to do, is get on and try and get an agreement but, if we can't get an agreement, get ready to come out anyway.
"It's by getting ready to come out anyway that we have greatly strengthened our position with our friends and partners in the EU, because they see that we are serious."
His comments come as Opposition MPs plan how they can block a no deal Brexit and courts prepare to hear cases aimed at stopping the suspension of Parliament.
Cases are due to be heard in London, Belfast and Edinburgh following outrage at what is being labelled an anti-democratic prorogation of Parliament.
The High Court in London will hear a case on Thursday brought by campaigner Gina Miller and backed by Labour deputy leader Tom Watson and former Conservative prime minister John Major.
Mr Watson said: "Proroguing Parliament is an unprecedented affront to democracy.
"The rights and freedoms of our citizens have been vandalised. This is an abuse of power that can and should be stopped."
He added: "I will be joining the judicial review launched in the High Court by Gina Miller and supported by John Major as a claimant."
Mr Major said on Friday he would "seek the Court's permission to intervene in the claim already initiated by Gina Miller, rather than to commence separate proceedings".
Liberal Democrat leader Jo Swinson also announced she would be joining the High Court action.
She said: "The attempt to shut down Parliament is an anti-democratic, authoritarian power grab by Boris Johnson, who wants to silence the people and their representatives.
In Scotland claimants were denied an interim block of the suspension of Parliament at the Court of Session in Edinburgh.
A cross-party group of MPs and peers filed a petition at Scotland's highest civil court earlier this summer aiming to stop the Prime Minister being able to prorogue Parliament.
They called for an interim interdict on Thursday to halt prorogation until a final decision has been made on the case.
On Friday, Judge Lord Doherty dismissed the action ahead of a full hearing set for Tuesday, September 3.
He said: "I'm not satisfied that it has been demonstrated that there's a need for an interim suspension or an interim interdict to be granted at this stage."
He said he was moving the full hearing from its original September 6 date to Tuesday, adding: "It's in the interest of justice that it proceeds sooner rather than later."
The PM said his decision to request that the Queen suspend Parliament was to allow the government to press on with domestic policy aside from Brexit.
"I said on the steps of Downing Street, I said we weren't going to wait until October 31, I said we will not wait before getting on with the priorities of the people of this country," he said.
He claimed MPs opposed to no-deal Brexit will have "ample opportunity between now and the 31st" to express their views.
Protest organisers are hoping "hundreds of thousands" of people will take part in disruption across Britain this weekend in response to the Prime Minister's plan to prorogue Parliament.
Labour leader Jeremy Corbyn encouraged his MPs to join the public protests.
He said: "There are also public protests across the country this Saturday, there will be a rally in Parliament Square on Tuesday evening, and I encourage Labour MPs to be present and to share our message."
Anti-Brexit campaign group Another Europe Is Possible has organised 32 #StopTheCoup demonstrations to take place in England, Scotland and Wales on Saturday.
Meanwhile, left-wing group Momentum is calling on its members to "occupy bridges and blockade roads" in conjunction with the protests.
Michael Chessum, national organiser for Another Europe Is Possible, told the PA news agency that "disruption is the only form of leverage protesters can rely on".