Obviously some were reluctant to tell the government even then

[sami]

Thanks for the answer Viktoria. I hadn't realised the distinction between those two words before.

.....just goes to show you learn something every day 

sami

[andrewalston]

Both suffragists & suffragettes arranged a boycott of the census to show their displeasure at the government's reluctance to move in the sensible direction. As a national event, it was seen as a good target.
"If women don't count, neither shall they be counted" said the placards.
“No Vote, No Census. If I am intelligent enough to fill in this Census form, I can surely make a "X‟
on a Ballot Paper. [signed Louisa Burnham.]” says one form visible on the National Archives website.
Emily Wilding Davison, who was later killed by the King's horse at the 1913 Derby, famously got herself enumerated as a resident of the Houses of Parliament.

[Viktoria]

 Thank you Andrew,that has made it very clear,  I was not absolutely sure.
  It will account though for some women missing from the 1911 census, won`t it.
  May be of help to some searchers even just as a possibility.
 Thanks again. Viktoria.