Theresa May promised to deliver a Brexit - but here is why we shouldn't be so sure

Theresa May is about to become Britain's new prime minister but do not be so sure that she will deliver a Brexit as promised.

The current Home Secretary is set to be confirmed as David Cameron's successor on Wednesday evening after Andrea Leadsom dropped out of the Conservative Party leadership contest on Monday afternoon.

One of the reasons Leadsom was able to mount a challenge to May was the positive effect that her pro-Brexit campaigning had on her popularity. May, however, campaigned for Britain to remain in the EU.

Nonetheless, speaking in Birmingham on Monday morning, May said that "Brexit means Brexit" and promised that she would make a success of it.

As social media users pointed out, though, "Brexit means Brexit" was a very vague statement. It did not even begin to indicate any form of time scale for when the country will leave the 28-nation bloc, or what post-Brexit Britain will look like.

When will May trigger Article 50?

For the UK to officially begin the process of withdrawing from the EU, the prime minister must invoke Article 50 of the Lisbon Treaty. Leadsom promised that the period between the referendum result and Article 50 being triggered would be "as short as possible," but May has not made this promise.

In fact, Brits who voted Leave should not expect to see the country withdraw from the 28-nation bloc until 2019 at the very earliest under May's leadership.

In an interview with Robert Peston earlier this month, May said (emphasis ours):

"I don't think it's possible to say that there is an absolute deadline [for Article 50 to be invoked]. What is important is that we do this on the right time scale and we do it to get the right deal for the UK.

"I've said that we shouldn't invoke Article 50 immediately. It shouldn't before the end of the year. We need to establish our own negotiating position. What's important is that we get the right deal and that's a deal which is about controlling free movement but it's also about ensuring that we've got the best deal possible in trade of goods and services."

Given that the Article 50 process lasts two years - and can be extended if necessary - it looks like Britain won't actually leave the EU until at least 2019 . But, Leavers will probably have to wait even longer.

One reason for this is that crucial elections will take place in France and Germany in the summer of 2017. Given that both are key players in the EU, it would be wise for May to wait until this electoral cycle is over so that she won't have to struggle to negotiate with leaders whose minds will obviously be elsewhere.

Another is that it is extremely unlikely that the UK will be able to establish its negotiating position in just a few months. Business Insider spoke to constitutional expert Peter Catterall last month, who predicted that Article 50 probably won't be triggered until 2018 because the government will require this length of time to clarify what deals it can reach with other countries.

May seemed to echo this when she claimed that the UK must secure the "right deal" before it activates Article 50. With this in mind, she might not lead the country out of the 28-nation bloc until 2020 or beyond.

You can see May discuss Article 50 in the clip below.

What will May's Brexit look like?

Like many senior politicians, May has been rather vague on the issue of post-referendum negotiations. Speaking in Birmingham on Monday, she reassured pro-Brexit party members that "Brexit means Brexit" - but what does this actually mean? 

Here is an excerpt from a speech May gave in April about negotiating with the EU in the scenario of Brits voting to leave the bloc. It won't fill Leavers with too much confidence:

This speech implied two things:

1) May preferred the country to remain in the single market if it voted to leave the EU.

2) But she had serious doubts about whether a future government would be able to secure the type of Brexit which many pro-Leave MPs desire i.e. the UK remains in the single market but does not sign up to the Freedom of Movement Act. 

May had every right to be skeptical, as multiple EU officials have already told the UK that it should not expect to be given exception from free movement rules in addition to access to the single market. Current European Council President Donald Tusk reiterated this stance last week when he said that the UK cannot enjoy the free market "à la carte" - a phrase that means that Theresa May will not be able to negotiate a deal based on single market access without freedom of movement or even cherry pick what Britain wants to keep or denounce from EU membership.

So, what will Brexit actually mean?

Theresa May was lauded by MPs from both sides of the referendum debate for taking a firm stance on the UK's withdrawal from the EU. However, what awaits her is a long, grueling process which will be much less straightforward than her claim that "Brexit means a Brexit" suggested.