Seen recently in a newspaper cutting dated Tuesday April 4th 1911:
THE CENSUS
THE SUFFRAGIST RESISTANCE
"The task of the enumerators this year, in addition to its natural increase through the growth of population, has been complicated by the tactics of the Suffragists, who declared their intention of refusing to be included in the returns as a protest against their exclusion from the suffrage, and took special measures to evade registration.
A considerable crowd gathered on Sunday night in Trafalgar-square, consisting almost entirely of men, chiefly young men, and at midnight the number of Suffragists in the Square was insignificant. Most of those present were in holiday mood, and small groups of Suffragists were surrounded and escorted by spectators, who indulged in good-natured cheers and laughter. No attempt was made to hold a meeting or to deliver speeches, as it is illegal to do so in the Square after sundown. The night was fine overhead, but the atmosphere was damp.
At midnight Superintendent Wells, of the Metropolitan Police, who had charge of the arrangements, warned the women that it would be advisable for them to go home, as there was a rough element amongst the crowd, which might at any moment become inconveniently pressing in its attentions if the women remained on the scene.
Hundreds of Suffragettes assembled at Aldwych Skating Rink at one o'clock on Monday, and were joined by hundreds of young men, the proceedings at first being somewhat lively. The gathering was addressed by Suffragist leaders, and a concert followed. Before going home the women breakfasted at adjoining restaurants."
So, if you can't find your London ancestor when the 1911 Census is released, maybe he or she was involved. I don't know if there were any other such protests in other areas of the country, but it's entirely possible.