One Wednesday afternoon in May, when Barbara Weed’s 18-year-old son Tom was right in the middle of his A-levels, he abruptly left home. ‘Dear Family,’ said the note he left on the doormat. ‘I need to take an indefinite amount of time away from the family, so I’ve moved in with a friend. Please do not contact me. Tom.’

Tom and his girlfriend had become increasingly interested in an online community called Freedomain Radio (FDR), which invites discussion about philosophy, politics and personal freedom.

Unbeknown to Barbara at that time, a key topic of the site – whose members seem to be mostly in their teens and 20s – is the idea that ultimate personal freedom can be gained by cutting yourself off from any involuntary relationships (ie your family) and entering into completely voluntary ones (ie your new mates online).