By Li-mei Hoang LONDON (Reuters) - Security services group G4S has drawn up plans with Greece's central bank to keep the country's cash machines stocked in the event of a full-blown economic crisis, the company told Reuters on Monday. Andreas Paterakis, the head of southern Europe for G4S, also said the Britain-based company stored cash for a handful of major businesses last week as fears grew about the stability of Greek banks. "Tuesday, Wednesday and Thursday were critical, really critical," he said, referring to withdrawals of cash from Greek banks.