I know he was popular in Blake's 7, but I remember him more prominently in Children of the Stones. This series was imprinted in my mind at an early age because of it's frightening qualities. However, I loved it (that and The Ghosts of Motley Hall - both of which had Freddie Jones in it, who at 88 is still ticking along nicely) and have the series on DVD if I ever wanted to take a trip down memory lane.
Still, a sad day for B7 aficionados - RIP Gareth Thomas (Children of the Stones episode under cut below).
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