Boris Johnson and Jeremy Hunt have a large and challenging in-tray waiting for them in Downing Street.
- Britain will have a new prime minister at the end of this month after Conservative Party members elect a new leader to replace Theresa May.
- Former Foreign Secretary Boris Johnson is the current overwhelming favourite to win the contest, ahead of his successor Jeremy Hunt.
- Whoever wins will have a large in-tray of problems to deal with as Britain rapidly heads towards its latest deadline for leaving the EU on October 31.
- Here are the 5 biggest problems facing Britain's next prime minister.
1. Renegotiating Brexit
The most pressing issue facing Britain's next prime minister is the one that brought down Theresa May: Brexit.
Both candidates have pledged to renegotiate the Brexit deal that Theresa May agreed with the EU.
Johnson has said that he is confident of securing a new agreement. However, doing so will be incredibly difficult.
The EU's chief Brexit negotiator Michel Barnier has repeatedly said the withdrawal agreement will not be renegotiated, and Theresa May's own attempts to tweak the agreement earlier this year were mostly unsuccessful.
Some Conservative members of parliament believe the problem was May herself.
"May never really tried to renegotiate the deal," one senior Brexiteer told Business Insider.
For his own part Johnson has insisted that he will "look into the eyes" of EU negotiators and use the threat of leaving without a deal to force them into a new agreement.
However, others are more sceptical.
One Conservative MP who visited representatives of EU member states in Brussels last month told Business Insider that "not a single one indicated any likelihood of the withdrawal agreement being opened."
2. Preparing for a no-deal Brexit
Because of this, the prospect of a no-deal Brexit is growing significantly, with Johnson insisting that he will take Britain out of the EU on October 31 "do or die."
The Former Foreign Secretary said that Britain must prepare to leave the EU without a deal, both as a practical necessity, but also as a negotiating tactic.
However, preparing for a no-deal Brexit will be very difficult, both logistically and politically.
As Business Insider revealed earlier this year, much of the warehouse space needed to prepare for a no-deal is no longer available.
The government departments in charge of Brexit preparations have also suffered an exodus of senior staff members in recent months.
Joe Owen from the Institute For Government think tank told Business Insider that the next prime minister will "come in and quickly realise the big risk is that we'll be less ready in October than we were in March."
Businesses could be reluctant to prepare again for no-deal after it was twice averted earlier this year.
"They've seen government cry wolf twice before," Owen told Business Insider.
"They'll be seeing Boris saying the odds of no deal are a million to one against and MPs saying they want to stop no deal — that's the stuff that will stick," Owen said.
"They are saying 'we've been here before and it didn't happen, why would we spend money again doing it?
It is also difficult to see how Britain's next prime minister could secure enough support from parliament to allow a no-deal Brexit.
An incoming prime minister could ultimately opt to suspend parliament, in order to force through Brexit. However, doing so would be politically explosive and may not even be possible.
Just this week, rebel Conservative MPs inflicted a heavy defeat on the government, when they voted for an amendment designed to prevent the next prime minister from suspending parliament in order to force through a no-deal Brexit.
The measure, which passed by a majority of 41, secured the support of large numbers of Conservative rebels, with several current government ministers also abstaining.
While the vote does not in of itself prevent a no-deal outcome, it is a clear signal of Parliament's intent to do whatever is required to prevent Britain's next prime minister from forcing through a no-deal.
3. Getting ready for a general election
The British Parliament has repeatedly voted against either leaving the EU with a deal, or leaving the EU without a deal.
Given both Hunt and Johnson have promised to deliver Brexit no matter what, they may ultimately have little choice but to go back to the country and hold a general election.
Conservative MPs really, really don't want to do that however. The party is currently experiencing historic lows in the opinion polls and came in a disastrous fourth place in the recent European Parliament elections.
With so many voters who backed them at the last election fleeing to the Brexit Party and the Liberal Democrats, almost no Conservative MPs are keen to rush into another vote.
"We've only been in parliament for two years," one Conservative MP who was elected for the first time in 2017, told Business Insider.
"We want to fix Brexit first. The last snap general election didn't work out too well."
Another Conservative MP said an election would only happen if parliament brought a no-confidence vote against the next prime minister in order to prevent a no-deal Brexit.
Forced to choose between the risks of a chaotic Brexit or a general election, parliament may ultimately choose the latter.
"The only reason an election will happen soon is if the government falls," said the MP. "We cannot go to the electorate as a matter of choice before that."
Aside from low levels of support, a snap election would also present challenges for candidate selection and funding, especially as many donors have deserted the party over its failure to deliver on Brexit.
Johnson, for his part, has denied that he plans to call an election. "It would be absolutely crazy for any of us to think of going to the country and calling a general election before we get Brexit done," he said at a leadership hustings in June, insisting that parliament could agree on a deal.
However, it was reported this week that Johnson's allies are preparing for an early election.
"You will need to get the party in fighting shape as early as possible," one campaign figure told The Times newspaper. "One of the reasons for the lack of success in 2017 was a lack of preparation. You need to pull things together."
And if the Conservative party experiences a surge in the polls following Johnson's election, the temptation to go back to the country could be too much to resist.
4. Opening Britain's purse-strings
When May first became prime minister, she pledged to tackle "burning injustices" in the country such as income inequality, the lack of affordable housing and the crisis in social care.
However, instead of dealing with these issues, her premiership has been entirely dominated by Brexit, with little significant domestic legacy to speak of.
Both Johnson and Hunt are determined not to make the same mistake and have announced a range of bold, and expensive, domestic policies.
Johnson has promised to cut tax for high earners, do away with tax on sugar-sweetened drinks, and put 20,000 additional police officers on the streets by 2020.
Hunt meanwhile has said he will slash corporation tax from 19% to around 12.5%, increase spending on defence, and award tax breaks to people who care for elderly relatives.
This string of expensive pledges has led to both coming under fire from across the political spectrum for making unrealistic spending promises.
Chancellor Philip Hammond warned that the damage caused by a no-deal Brexit would leave no money to pay for such pledges, with the independent spending watchdog, the Institute for Fiscal Studies, also criticising the plans.
Passing such plans through parliament would also be difficult, given that the Conservative government currently has a tiny working majority of just five MPs.
As a result there will almost certainly be a sizeable gulf between the next prime minister's campaign promises, and what they actually achieve once in power.
"What you're going to see is a lot of bold policies but less than bold legislation," one former Conservative Cabinet minister told Business Insider.
5. Dealing with Trump
Both Johnson and Hunt have significant experience as Foreign Secretary dealing with President Trump and appear to have a decent personal relationship with him.
During his recent state visit to the UK, Trump praised both men.
Comparing them favourably to May, Trump tweeted in early July that it was "good" that Britain would soon be getting a new prime minister after the "mess" that May has made of Brexit.
Johnson has also praised Trump, insisting that the president has "many, many good qualities," and "talks sense."
The former Foreign Secretary is expected to make an early trip to the US should he become prime minister.
However, Trump is highly unpredictable. His recent attacks both on May and her ambassador to the US Kim Darroch, have strained relations between the two countries and created a serious diplomatic crisis.
On other foreign policy issues, the two countries are also at odds. The UK was at the forefront of efforts to bring Iran back into the international community through the Iranian nuclear deal, whereas Trump has been instrumental in dismantling that agreement.
Both Johnson and Hunt have also made securing a trade deal with US, a key part of their post-Brexit plans.
However, any such deal would be hugely controversial, given that it would likely include provisions on food standards and the NHS
During his recent state visit Trump insisted that the NHS must be "on the table" in talks, before later backtracking.
Whatever happens, managing Britain's relationship with Trump's White House will form a major part of the early days of any incoming prime minister.