Watch: What Theresa May wrote in the UK's Brexit letter

Theresa May's Brexit letter to European Union President Donald Tusk will please EU leaders by sounding constructive and acknowledging Britain must settle obligations before leaving. But the prime minister also made some tougher demands.

In the six-page document delivered today to the EU summit chair to trigger a two-year countdown to withdrawal, she called for parallel negotiations on not just divorce terms but a new trade pact and special deals in key sectors. She also made a veiled threat on security cooperation if talks break down.

"We should engage with one another constructively and respectfully, in a spirit of sincere cooperation," May wrote.

She referred -- twice -- to London's "obligations as a departing member state", in a nod to Brussels' demands that a "Brexit bill", possibly of the order of 60 billion euros, be paid to cover outstanding commitments before Britain leaves.

She echoed the EU's own language in acknowledging that there could be "no cherry-picking" to retain the best bits of EU membership and acknowledged that Britons doing business with the Union would have to abide by rules they no longer help to set.

In response, the other 27 governments said Britain...