It is actually very reassuring to know that there are no reliable statistics on the issue of how many home educators there are in the UK. The search facility on the official website for results from the last UK Census finds no entry for either home education or home schooling. Being left alone in this way is how it should be. On the other hand, it could be encouraging to know something along these lines:
"the U.S. Census Bureau in 2001 reported that more than 2 million children were being homeschooled in the United States. More astonishing: that number was rising at a rate of 15 to 20 percent a year".
Given that in 2003, there were 73 million children under the age of 18 in the U.S. with, say, a growth rate of home educators by 400,000 per year, it will take approx 182 years for the whole of the population to be home schooled. That doesn't account for a tipping point though; cascades of children would pour out of school if they knew their friends could do it too.