I would agree with Nivard that literacy rates were low in 1851.  Prior to 1840, most schooling was strictly religious.  Literacy was not the goal, morality was.  Many people could write their name, but if they got a letter, they had to have the vicar read it for them.  Secular education became a social issue around 1840, but it took a while to get anything like a modern school going in most parishes.  A Royal Commission in 1861 found that most boys left school by age 10 or 11, particularly in agricultural areas. Add to this the belief in many Englishmen that the "Government" didn't need to know anything about them, and I'm surprised that the census is as accurate as it was.     Lou Mills