This tweet by Rory Cellan-Jones sent me to Twittercounter, which produced this chart:
Suggests that something strange is going on. Compare, for example, with the chart for my account, which accurately reflects data coming from email notifications from Twitter.
Hmmm… Is a spambot signing up ‘followers’ of Rory?
LATER: Now he’s back to his original track.
Which suggests that there’s something wrong with Twittercounter?
Moral: put not your faith in these statscounting services.