Tory leadership: Jeremy Hunt sets September deadline for no-deal decision
The Foreign Secretary made the pledge as he set out a 10-point plan for delivering Brexit, including making £6bn available to support farmers and fishermen who would be worst hit by a drop in exports to the EU.
Mr Hunt said that if he did not think there was sufficient movement from the EU by the end of September, he would increase efforts to cope with a no-deal exit on 31 October.
"We won't blink as a country. That no-deal Brexit is not going to be an opportunity for them to successfully turn the screws on our country.
"I will start engaging with the EU straight away, throughout August.
"Then, when we have published our plan for a deal we think we can get through Parliament by the end of August, we will start formal negotiations in September."
Mr Hunt added: "There is a hard deadline in what I have said, by the end of September, I, as Prime Minister, will make a judgment as to whether there is a realistic prospect of a deal that can get through Parliament in the short-term.
"And, if my judgment is that is not the case, talks will stop and we will put our heads down and focus on no-deal."
Under Mr Hunt’s plan, food producers would be treated like the financial services industry during the 2008 financial crash through a temporary No Deal Relief Programme.
He also set out plans to create a Cobra-style emergency committee to "turbocharge" Whitehall preparations for no-deal and keep Britain open for business in the event of World Trade Organisation (WTO) tariffs coming into effect.
"You cannot leave the European Union on a wing and a prayer," Mr Hunt said in a speech in London. "Britain deserves better."
Mr Hunt said: "If you're a sheep farmer in Shropshire or a fisherman in Peterhead I have a simple message for you - I know you face uncertainty if we have to leave the EU without a deal.
"I will mitigate the impact of no-deal Brexit on you and step in to help smooth those short-term difficulties.
"If we could do it for the bankers in the financial crisis, we can do it for our fishermen, farmers and small businesses now."
A No Deal Brexit Budget will also be prepared, including a corporation tax cut to 12.5%, increasing the annual allowance to £5 million and taking 90% of high street businesses out of rates.
He stressed he would prefer the UK to leave the EU with a "new deal" that removes the Irish backstop and ensures a fully independent trade policy, which he said is possible "if the Commission engages in good faith".