British Prime Minister Theresa May on Tuesday signed the historic letter that will launch Brexit when it is delivered to Brussels on Wednesday, a photo released by her office showed.

Sat in front of a lone Union Jack national flag and a portrait of Britain's first prime minister, Robert Walpole, a serene-looking May signed the letter to begin the country's departure from the European Union.

The letter will be taken from 10 Downing Street to Brussels, where it will be delivered by Tim Barrow, Britain's EU ambassador, to EU President Donald Tusk around 1130 GMT on Wednesday.