Prime Minister Boris Johnson is playing down the possibility of a Brexit breakthrough, telling people “not to hold their breath”.
Mr Johnson, who met German Chancellor Angela Merkel and French President Emmanuel Macron this week, said talks were making progress but it would not be easy to persuade the European Union.
The main stumbling block is the backstop, which was intended to be used to avoid the return of a hard border between Ireland and Northern Ireland if a UK-EU trade deal is not reached.
Mr Johnson wants it removed from the deal offered to his predecessor Theresa May but the EU is standing by it.
He said persuading Brussels to change its stance would “take some time”.
The prime minister told reporters in Devon: “They [Mrs Merkel and Mr Macron] could see that we want a deal, they can see the problems with the backstop.
“Clearly, Angela Merkel thinks that the solutions can be found within 30 days – actually what she meant was if you can do it in two years, you can certainly do it in 30 days.
“But I want to caution everybody, okay? Because this is not going to be a cinch, this is not going to be easy. We will have to work very hard to get this thing done…to persuade our EU friends and partners, who are very, very, very hard over against it, will take some time.
“I’m afraid we will have to prepare to come out without an agreement and we can do that, we are very confident that we will be okay because we will have all sorts of preparations in place.”
He added: “We are making progress but I am just telling people not to hold their breath, because I have seen the way these Brussels negotiations work.”
Meanwhile, European Union Brexit negotiator Michel Barnier said he was ready to examine “realistic” proposals from Britain regarding its departure from the bloc.
He wrote on Twitter: “We are ready to analyse UK proposals that are realistic, operational and compatible with our principles.
“EU wants an orderly withdrawal but is ready for any outcome.”