This question has been settled with a final result: "Q1 2017". Trading has finished.
When will the Brexit happen? Will it happen at all? Will British politicians abide by the result of the referendum or will they ignore it?
In a national referendum on 23 June 2016, a majority of 51.9% of British citizens voted to withdraw from the European Union ("Brexit). An immediate second Brexit referendum was demanded by an online petition but swiftly ruled out by UK government. (2)
For more background: Wikipedia
As the next step, the UK government has to notify the European Council formally of the UK’s intention to withdraw from the EU, as required by Article 50 of the Treaty on the European Union. (1)
It is uncertain if and when this notification will be realized. The UK's incumbent Prime Minister David Cameron stated that the withdrawal negotiations - thus the formal notification - will be the next Prime Minister's task. His successor will be determined at the UK Conservative Party leadership elections in October 2016. (3)
On 11 July 2016 David Cameron announced he will leave Downing Street 10 two days later. Home Secretary Theresa May will succeed him in Office. (5)
Britain triggered article 50 on the 29th of March, for more information go here.