Sabeel Ahmed, 26, of Liverpool, was charged on Saturday with failing to disclose information that could have prevented an "act of terrorism".
Earlier the same day, Australian police charged Mohamed Haneef, Sabeel's second cousin, with "providing support to a terrorist organisation".
Bilal Abdulla, a 27-year-old doctor who trained in Iraq, was charged in Britain last week with conspiring to cause explosions.
A seventh man, Kafeel Ahmed, 27, an Indian engineer who is Sabeel's brother, is under police guard in hospital after being badly burned when a sport utility vehicle was driven into an airport terminal building in Glasgow, Scotland, and set ablaze on June 30.
That attack came 36 hours after the discovery of two cars packed with fuel, gas tanks and nails in central London.
Police think the two incidents were linked.
All but one of the eight original suspects are medics.
Dana Asha - the wife of Mohammed and the only woman among those detained in the case - was arrested at the same time as her husband, but was released without charge on Thursday.