Four years ago on Tuesday, the UK voted to leave the European Union. But the negotiations continue to rumble on.

Here is a look at the current state of play, where talks are headed and where they may hit sticking points.

– Where are we now?

Brexit formally took place on January 31, but the UK is still in the transition period in which it follows EU laws and benefits from single market membership until the end of the year.

The two sides are trying to thrash out an agreement on a future relation to include an ambitious free trade deal.

But after four rounds of negotiations amid the coronavirus crisis, Boris Johnson and EU leaders including Commission President Ursula von der Leyen held a virtual summit in order to break the deadlock.

Though the formal deadline for the request is the end of the month, the UK has formally told the bloc it will not be extending the transition, adding extra pressure to resolve the talks by 2021.

– So what happens next?

Both sides have agreed that “new momentum” is required to reinvigorate the talks being led by David Frost for the UK and the EU’s chief negotiator Michel Barnier, who have agreed to “intensify” discussions in July.

Having been hindered by the constraints of teleconferencing, the negotiating teams hope to be able to meet in person if the coronavirus conditions permit.

The next week of talks are planned for Brussels on June 29, before alternating between the Belgian capital and London.

– And what happens if they never see eye to eye?

A senior member of the UK negotiating team has said talks could not be allowed to drag on into the autumn without clear evidence that a deal was possible.

Ceasing negotiations would lead to the result everyone says they want to avoid – the UK crashing out of the bloc in a disorderly exit.

While the Government insists it is not a “no deal” Brexit because of the Withdrawal Agreement brokered last year, business leaders are very concerned about leaving without a trade agreement on January 1.

CBI deputy director-general Josh Hardy warned: “Failure to break the deadlock only leaves a choice between an extension that the UK Government has already ruled out or worse, a deeply damaging no deal.”

In a significant U-turn, however, Cabinet Office minister Michael Gove has said that full border checks would not be immediately imposed, with a phased approached instead being used over six months.

– What are the main stumbling blocks?

Two of the key issues on which the sides are struggling to find agreement relate to fisheries and the so-called level playing field.

The EU wants to see the status quo maintained for fishing access and quotas, but the UK Government wants Britain to have controls of its own waters.

And on the level playing field, which is aimed at preventing the UK from undercutting EU standards on issues including workers’ rights, environmental protection and state subsidies, Britain believes Brussels is trying to bind the UK to EU law.

Mr Frost has said the EU must “accommodate the reality of the UK’s well-established position on the so-called ‘level playing field’, on fisheries, and the other difficult issues”.

There is also disagreement over the governance of any future agreement, including the role of the European Court of Justice.

Ensuring no return to a hard border on the island of Ireland also remains an extremely sensitive issue.

– What would a ‘no-deal’ look like?

If no agreement is reached, and the transition period is not extended, the UK will leave under World Trade Organisation terms at the end of the year.

This would lead to tariffs and quotas on goods coming from the EU to the UK and vice versa, and there would likely be border checks.

Many are fearful of the impact of a no-deal on the economy, fearing it could compound the chaos inflicted by the coronavirus crisis.