Image source, AFP

In case anyone was wondering, the rest of the European Union is well aware that this moment was coming.

The UK government announced that it would invoke Article 50 today about a week ago and Mrs May talked to key players in a series of phone calls last night, including German Chancellor Angela Merkel and European Commission President Jean-Claude Juncker.

Mr Juncker, who has described the UK's exit as a tragedy, described the conversation as "good and constructive".

Norman Smith
Assistant political editor

Chancellor Philip Hammond has signaled that there will be no cut-off from today to the rights of EU nationals arriving in Britain.

He said Britain would continue to remain a full member of the EU for the next two years and would observe "the same rules and obligations".

The European Parliament has threatened to veto any agreement if the UK had ended those rights from today.

Mr Hammond also played down the prospect of Britain leaving the EU without any deal, insisting "we will get a deal".

And in what appeared a rebuff to the Foreign Scretary Boris Johnson he suggested the UK would have to compromise with other EU countries and could not expect to secure all its demands.

"We cannot have our cake and eat it," he said.

Mr Hammond also appeared to hint at some partial or associate membership of the single market. He repeatedly stressed that the UK could not remain "full members" of the single market.

Today Programme
BBC Radio 4

Mr Hammond rounds off the interview by saying this is an important moment in the Brexit journey, but just a step in the process.

The BBC's political editor Laura Kuenssberg says we learnt quite a lot from the interview, not least the chancellor's views on what sums the UK may have to hand over and whether the UK could achieve everything it wanted.

Dismissing talk of "having your cake and eat it" seemed to be a rebuff to certain Brexiteers, including Boris Johnson, who have used the phrase.

However, she says the most significant line was him appearing to rule out the possibility of Wednesday being the cut-off point in terms of EU residents in the UK being allowed to remain - something which has been suggested in the past.

Experts say there will have to be a deadline after which arriving EU residents won't have the automatic right to work or to live and work in the UK, but we don't know yet when that will be.

Today Programme
BBC Radio 4

BBC Radio 5 live

BBC Radio 5 live's Tony Livesey  asked 50 people - from all walks of life - whether leaving the European Union would make Britain a more tolerant country. 

"There's a different between racist and being loyal to your own country," said Leave voter David Williams. "We want people to come and improve our country."

Today Programme
BBC Radio 4

Chancellor Philip Hammond seems to be slightly taken aback when Nick Robinson asks him whether he has actually seen and read the letter, replying "of course I have".

He says he was involved in its drafting and rejects claims he has been "marginalised" in recent weeks since the embarrassing Budget U-turn on National Insurance rises. 

The chancellor says the letter will expand slightly on what the government has already said about its aims, "expressing further" what it wants from the negotiations and how it sees then developing.

The tone of the letter will be important in sending a signal about how the UK intends to conduct the negotiations, he adds.

Today Programme
BBC Radio 4

Asked about reports that the EU is seeking £50bn from the UK by way of a "divorce bill", Mr Hammond says he is not surprised that such "aggressive" figures are being cited ahead of the start of negotiations.

While the UK will go about discussing the "rights and obligations" stemming from its continuing membership in a "business like" manner, he insists he does not recognise the kind of numbers which are being bandied about".

Today Programme
BBC Radio 4

Today Programme
BBC Radio 4

The UK will look to negotiate an early deal to "protect" the rights of Britons living on the continent and EU nationals in the UK, he says.

However, Mr Hammond stresses that there needs to be a reciprocal agreement on both sides. 

Today Programme
BBC Radio 4

There will be "give and take" in the negotiations, Chancellor Philip Hammond says.

Having ruled out membership of the single market and customs union, the chancellor accepts there will be "consequences" from that.

The UK recognises that it cannot "cherry pick" what it wants or, in his words, "have its cake and eat it". However, he believes that similar customs arrangements to what the UK enjoys at the moment can be negotiated. 

As the government formally triggers Article 50, BBC editors set out the key negotiation areas.

Emma Midgley
BBC South

The MP for Wokingham, John Redwood, has told Andrew Peach on BBC Berkshire this morning there is nothing to fear from the EU after Brexit.

He said: "We have absolutely no need to pay them a great big one off payment, we have no need to give in on controlling our boarders in a sensible way, they will come round to see they need that tariff free access to the UK market, which is really Eldorado for them - they will see no need to put that at risk."

Today Programme
BBC Radio 4

The chancellor says it is an exciting moment for the UK which he believes can forge a "global path" in the future outside the EU. 

He has no doubt that a deal will be struck but what matters is getting the best possible agreement for the UK.

He says the UK's EU partners have been talking in a "sensible and constructive" fashion and he is confident that a "pragmatic" deal can be secured.

It is in everyone's interest to get a deal that protects their own national interests and the idea that there will be a "worse care scenario" of no deal is "just ridiculous". 

Today Programme
BBC Radio 4

Image source, PA

Chancellor Philip Hammond is being interviewed on BBC Radio 4's Today.

He says this is a "pivotal moment" for the UK. He urges people to "put the divisions of the past behind us" and focus on the opportunities available to the UK as it seeks to move ahead.

"We are all on the same page. We are all seeking the best possible deal". 

BBC Breakfast

Tory MP Bernard Jenkin says the "disaster scenarios" predicted by some of those who want to remain in the EU about what lies ahead are "just ridiculous".

Mr Jenkin says there will be agreements on a whole range of issues, including security, citizens rights and transport.

He says the idea that people will wake up the day after Brexit and find "you aren't able to get a plane from Heathrow to Paris" is just nonsense. 

Image source, PA

It is more than nine months since the UK voted to leave in a referendum by a margin of 51.9% to 48.1%.

Since then, there have been endless debates in Parliament about the likely shape of Brexit and a legal challenge over the involvement of MPs and peers which made it all the way to the Supreme Court.

Now that the big day has arrived, Labour says the focus should move from issues of process to substance.

Keir Starmer, its Brexit spokesman, says the government must get the "right deal" for the UK. 

BBC Newsnight

Image source, AP

This is the man who will actually deliver the Article 50 letter, which effectively puts the EU on notice that the UK will be leaving.

His name is Sir Tim Barrow and he is the UK's permanent representative to the EU - effectively our ambassador to the EU.

The career diplomat only got the job in January when his predecessor resigned unexpectedly so it is a rather big day for him.

He is expected to hand the letter to Donald Tusk, the head of the European Council who will be representing the other 27 states.

Mr Tusk, a former Polish prime minister, is expected to tweet an initial response soon after receiving it.