The run-through done for the first time was named ‘Castle Dove’ had Theresa May’s senior cabinet ministers and Whitehall officials went over ‘D+1’, the day after The Queen dies.

the protocol was completed on an “unprecedented” scale according to The Sunday Times.

A source told The Sunday Times: “This is the first time different ministers have come together in one room. Previously it has only been officials.

Ministers practise procedures for The Queen’s death

http://royalcentral.co.uk/uk/thequeen/ministers-practice-procedures-for-the-queens-death-105472

Moar notes from additional articles

The run-through, apparently known as Castle Dove, saw Cabinet ministers and Whitehall officials discuss "D+1", the day after the monarch's death, said the Daily Mail.

The run-through apparently focused on 'D+1', the day after the monarch's death

Cabinet ministers reportedly joined Whitehall chiefs to prepare for the first time

It came in the week that the Queen pulled out of a service at St Paul's Cathedral

http://www.dailymail.co.uk/news/article-5905731/Ministers-rehearse-Queens-death-time-secret-exercise.html

www.nzherald.co.nz/lifestyle/news/article.cfm?c_id=6&objectid=12081342

side note

‘London Bridge’ is the code name for the plans that will take place from when The Queen dies to her funeral