County Councillor “defects” to LibDems

Independent County Councillor for Bishops Lydeard (more properly Lydeard Division) announced today he is to join the LibDem group on Somerset County Council. I am not quite sure if defect is the right term. Can you defect from being an Independent?
Without taking anything away from the LibDems (or any other political party on Somerset County Council) this is a sad loss. Cllr Rigby provided a firm, intelligent, non-partisan voice in the Council Chamber. Sometimes it looked like the lone voice crying in the wilderness. To lose that independent voice will surely be to the detriment of the council as a whole.
However Cllr Rigby has clearly weighed up the pros and cons. He says “I have reached the position where some of the things I want to achieve for our community can best be delivered as a member of a major political group.” And as he decided the LibDems were pretty closely aligned to his own views, in particular on Brexit, he has joined them.