New data suggests that up to 600,000 users failed to login to their Facebook accounts in the UK over December.

Ranked at number six in the territories with the largest number of Facebook users, the UK was the only country in the top 10 to show a decline over the festive period, representing a 1.86% drop.

Social media statistics company SocialBakers was reported in the Guardian as finding 33 million unique users accessed Facebook in the UK in December, which comScore describes as 53 percent market saturation; second only to the U.S., which has a 54 percent saturation rate and 169 million unique users per month.

However, SocialBakers has put up a clarification of the figures on its Web site. The company said that the statistics need to take into account the fact that 15 percent of the population, who are under 13, aren't allowed on Facebook and that 16.5 percent of people in the UK are older than 65 and typically not on Facebook.

"This effectively means that UK is inflecting in terms of numbers at near full penetration on Facebook (note: Not stagnating, nobody has yet done any proper seasonality analysis because of the growth social networks),"wrote Jan Rezab, CEO at SocialBakers. "I can't imagine their fans could grow by 10-20  million new users, although this depends if they allow teens under 13 on the platform and furthermore largely depends on their mobile adoption."

"This is especially important because Facebook measures by Monthly Active Users," he continued. "The monthly active user count is statistically vulnerable to more casual users of the platform, users that don't use it that often and might fall out of the 30-day range from time to time. And yeah, my grandpa might sometimes not be an active user on Facebook, even though he is using it."

Rezab also cautions against reading too much into the numbers since the complete data from Facebook's ad interface won't be available for several weeks, and that could increase the figure from December.