I am a believer and proponent of contingency plans for contingency plans, but this is ludicrous. Us the British would never put this Queen, especially at her age, at any risk. She is respected, admired and beloved. They might protest, mightily, around Parliament and Downing Street, but not outside Buckingham Palace. They also know that the Queen did her best. Brexit has nothing to do with the Queen.
This is not WW II and even then her parents, to their eternal credit, refused to leave London. There is no way this Queen is going to get bundled out of London. If you have been watching ‘Victoria’, on PBS, you will know that her husband made her leave London when there was potential trouble and she rued that she did so. She came back in a hurry. Well my Queen is not going to make that mistake. This is stupid. Wasted time.