The former head of the Diplomatic Service, Lord Ricketts, has taken ITV News through the hidden meanings behind Theresa May's six-page, 2,000-word letter signalling Britain's intent to leave the EU to Donald Tusk.
- The sticking point
"It is necessary to agree the terms of our future partnership alongside those of our withdrawal from the European Union."
"I was really struck to see the same sentence coming three times in this quite short letter," Lord Ricketts says.
"In other words, we can't sign a cheque for the money we may owe first, and then only later come onto the future partnership. That's not possible for a British government and she makes that very clear ... that's going to be the first row in the negotiation I think."
- The veiled threat?
"In security terms a failure to reach agreement would mean our cooperation in the fight against crime and terrorism would be weakened."
"I think it's a very strong marker and a reminder to people that we are a very important security partner and we have a very effective security service, we're very good on counter-terrorism and crime and she's saying her that a failure to reach agreement, of course, will weaken that cooperation.
"It's a statement of fact but it's also a very strong signal."
- The 'after-match' period
"...implementation periods to adjust in a smooth and orderly way to new arrangements."
"I think it's a recognition that we are not going to get everything fully sorted and clear within two years and there's going to be an 'after-match' period - possibly periods - where the detail gets sorted out."
- A surprise for the City
On proposals a new trade deal "covers sectors crucial to our linked economies such as financial services and network industries".
Lord Ricketts says this is new.
"It's a bit of a signal to the City and our IT high-tech industry and that that needs to be protected in some way as part of negotiations."