Brexit talks are back underway in earnest again, with European Commission chief negotiator Michel Barnier over in London for a change.

If you’re confused about where the talks are at the moment, here is an explainer to clear everything up.

What are they trying to agree now?

Since the start of the year the two sides have been trying to come to a deal on the transition period, or what is officially called the ‘implementation period’. This will start in March 2019 if everything goes according to plan, and will last about two years.

Issues that need agreeing with regards to the transition are things like whether the UK will get a say over EU laws, exactly how long the period will last, and whether free movement continues in full during the transition period. The UK wants some say over EU laws, is considering asking for a slightly longer period, and doesn’t want free movement rights to apply to citizens who move to the UK during the transition.

The UK looked set to agree to Brussels on all this until a few weeks ago, with David Davis appearing sanguine at a recent parliamentary committee. But Tory Eurosceptics who generally tell the Prime Minister what to do have kicked up a fuss and briefed Tory-supporting newspapers that a leadership challenge could be close. Following that, Downing Street has said that actually, they don’t agree with the EU at all.

Do any other issues need resolving?

Both the UK and EU – especially the UK – are also talking to their own sides about what they want the future trade relationship to look like. In Britain this takes the form of Cabinet rows and discussions within the Tory party. In the EU it is seminars to ask different countries what they want.

Unresolved “leftovers” from the first phase of talks – notably on citizens’ rights and the Northern Ireland border – also need to be agreed.

Didn’t they solve Northern Ireland and citizens’ rights in the first phase of talks in December?

No, they made “sufficient progress” on those issues to move to the next phase, but they haven’t been solved.

On Northern Ireland, the “solution” they came up with was essentially to say they would find a solution in the future, and a UK pledge to guarantee an open border. What that solution actually looks like in practice is not a lot closer than before.

Citizens’ rights looked closer to a solution, but the wound has been opened again after Theresa May said she would not guarantee citizens’ rights for anyone who arrives during the transition period. The EU wants the opposite.

What about trade talks?

Absolutely no discussions about the future trading relationship are taking place until the UK has decided what sort of trade relationship it wants. If it can decide soon, in March there will be talks about the trade framework, with emphasis on “framework”.

These are essentially scoping discussions. The EU has repeatedly said it expects the actual negotiations of a free trade agreement to take place during the transition period, after the UK leaves the EU – so from March 2019 onwards.

Can Brexit be reversed?

Why is everyone talking about the Customs Union?

Theresa May ruled out membership of the EU customs union in her Lancaster House speech at the beginning of 2017, around a year ago. However, two developments have put it back on the agenda: Firstly, a leaked analysis by the civil service shows leaving the customs union would be an economic disaster – and has led to some Tories, including a sitting minister, to question the wisdom of going through with this particular detail.

Secondly, many people read the preliminary agreement inked in December on Northern Ireland as effectively requiring the UK to stay inside the customs union. This is because the UK said it would prevent a hard border on the island of Ireland, but also one between mainland Britain and Northern Ireland, and a customs union with the EU appears to be the only way to do this.

Downing Street spent the last week prevaricating on this, but on Monday confirmed it would not stay in “The” customs union or even “A” customs union.

What’s the difference between “The” customs union and “A” customs union?

Mostly semantics. “The” EU customs union is what EU member are a part of, and also some places like the Isle of Man and Jersey that aren’t in the EU. It is an institution embedded in EU treaties.

Meanwhile “A” customs union is like what Turkey has – they haven’t signed any EU treaties, but they still have a common external tariff barrier.

Membership of both “The” and “A” customs union could be functionally the same thing, or “A” customs union could omit some areas, depending on what was agreed. The distinction is ultimately a red-herring.

Will there be a Brexit deal?