How do you renegotiate with a side that won't talk? And what key skills are needed to get what you want?
Theresa May is going back to Brussels for emergency talks after postponing Tuesday's seemingly doomed vote by MPs on her Brexit deal.
But the European Commission President Jean-Claude Junker has said there is “no room whatsoever for renegotiation”.
So how can you rekindle talks with a side that won't negotiate? What's the toolkit for a great negotiator? And what would be the worst thing to do?
ITV News asked some of the UK's top negotiators what skills are needed to secure a difficult deal.
How do you renegotiate with a party that doesn't want to talk?
European Council President Donald Tusk has joined Mr Juncker in insisting time has run out for Mrs May to renegotiate.
But former diplomat Carne Ross says negotiations are never off the table.
He told ITV News: "I think the thing is with the EU is that it's not over until it's over, you can always renegotiate. She doesn't need to say 'give me what I want or else'."
Clive Rich, one of the UK’s leading deal makers and author of ‘The Yes Book: The Art of Better Negotiation’, said Mrs May had to sweeten her offer to Brussels.
"I think the only way to pull this off is if the EU has an incentive, we really need to firm up the trade agreement," he told ITV News.
Top divorce solicitor Georgina Hamblin from law firm Vardags is familiar with expensive court cases having helped a client win a £64 million divorce settlement against the multi-millionaire boss of retailer Laura Ashley.
But when it comes to the billions of the EU divorce bill, she believes the prime minister should use them as bargaining chips.
"With financial deals like the £39 billion bill from the EU, you need to know what you are getting in exchange, otherwise it doesn't seem like a fair deal,” she said.
What's the secret to good negotiations - and what's the wrong approach?
Georgina Hamblin spent this week in an 11-hour negotiation for a client and believes the key to a good negotiation is being upfront with your needs.
She told ITV News: "The most important thing is to go in with a clear agenda and being completely transparent.
"There is so much doubt at the moment both by the public and in Parliament."
She suggested "not setting yourself an unrealistic timeline or boxing yourself in", adding: "(Mrs May) has showed her cards too soon."
Carne Ross suggested that being “flexible” can get you what you want.
He said: "I think in many ways it's good to not be macho and tell Brussels this is how the deal is going to go. There is 27 of them and one of us, you need to be flexible."
As the founder of the non-profit advisory group Independent Diplomat, he's negotiated for those in marginalised countries across the world.
"If I were her I would call France, Germany and Dublin and propose something that would slide in Westminster," he said.
"The best kind of offer has options and going back with alternatives might work."
So what skills do you need as a top negotiator?
No negotiator wants to risk looking weak or "desperate", as Labour leader Jeremy Corbyn described Theresa May’s move on Monday to postpone the 'meaningful vote'.
According to Clive Rich, Theresa May - like many others - won't have all the skills to bring about a final deal as she travels to Europe this week.
Although he describes the prime minister as "tenacious, determined and steadfast" based on her performance so far, he told ITV News: "There are very few people who are good at everything, there's a whole toolkit you need to negotiate."
He said that "flexibility" was also a fundamental thing that he believes the prime minister lacks.
"I think everybody is naturally good at negotiation but may have different skills. You can be good at building rapport but terrible at haggling, some are very assertive while others are good at listening," he said but to be a top negotiator you need to have a full range of skills.
He suggested there are no politicians equipped to prevent a no-deal Brexit.
"I can't currently see anyone with the full range of skills - part of the issue is negotiating with an ideology, things that they cling to ferociously," he said.
What happens if a negotiator changes at the last minute?
The uncertainty over Mrs May's Brexit deal has led to speculation her position as prime minister could soon end.
So what happens if a leader changes so late in key negotiations? Does that weaken the bid?
According to Clive Rich, it's not as damaging as it may seem.
"It doesn't matter who's fronting the negotiation,” he said - as long as a clear decision maker is identified.
"In negotiation it's better to have a referral power - someone who has the power to make the decisions," he said.
Rich said other shifts in negotiations can help.
"It's good to change the pattern, change the energy - where you meet, the layout of the room, who is involved.”
So how can tough negotiations ultimately be resolved?
With any negotiation, whether it is a divorce or a Brexit deal, the experts say discussions are helped when both parties know each other’s needs.
Georgina Hamblin says successful deals are made by: “Knowing exactly what your client wants."
She said that "can help you measure the best and worst possible outcome”.
Clive Rich advises that putting yourself second could be a win for everyone.
“Rather than focusing on what you want, you spend all your energy thinking about what could be in their interest,” he said.
And he cautioned: “I would not give them an ultimatum, you have to be subtle and careful with threats to retain your credibility."