By Adam Bloodworth The head of the Edinburgh Festival Fringe Society has warned the annual Edinburgh Fringe event is under “existential threat” due to rising costs faced by companies and venues. Speaking on Barry Fearn’s Leading Conversations podcast, Society chief executive Shona McCarthy said the lack of support had left the Fringe “cracking at the seams” before the pandemic. She said: “Pre-Covid, the whole ecosystem was already creaking at the seams. Then Covid hit and our entire income went in one fell swoop. “The Fringe came back last year, but with every single participant and organisati…