Prime Minister Theresa May does not have a strong hand to play at the Brexit negotiating table and as a result Britain may not leave the EU, Liberal Democrat leader Sir Vince Cable has said.
The Government is in a "complete pickle" over the negotiations and it is possible the planned exit date of March 2019 will not happen, he claimed.
Sir Vince, who became Lib Dem leader in the summer, also said the Brexit deal would be determined by the EU and the European governments, and not Mrs May and the Conservatives.
"We could get to the position where the Government is so unprepared, so disorganised, so divided, we just finish up in a year's time in a complete pickle and the Government looks for a way out," Sir Vince said.
"What we have forgotten is that in the last few months we have been having this big national debate about what we want but actually the terms of Brexit will not be set by the British Government, it will be determined by the European negotiators and the European governments.
"They will decide what kind of relationship we will have with them. We are no longer the demander in this situation.
"That's why I think, if the British Government is put in an impossible position, then it may well be all of this will unravel."
Sir Vince reiterated his call for a second referendum on the terms of the Brexit deal.
"One way out would be to do what my party are arguing, which is to have a public vote on whether to press ahead with all of this or do you want an exit from Brexit?" he said.
"It could be that the thing is such an absolute mess that we just don't go ahead."
Sir Vince, speaking during an event at the Cheltenham Literature Festival to promote his debut novel, Open Arms, said another option was that Britain ended up "half in and half out" and eventually, after a transitional period, decided to stay.
"People realise it is a bit ridiculous to be operating within the rules of the EU and having no say over it, so we find our way back into it," he said.
"It's all a bit messy but we finish up with a position not greatly different from where we are at the moment.
"You can think through perfectly plausible scenarios where Brexit doesn't happen."