HONG Kong leader Carrie Lam says she has to pile up cash at home as she has been unable to open a bank account in the global financial centre since Washington sanctioned her shortly after Beijing imposed a national security law on the city. Beijing circumvented Hong Kong's legislature and imposed a national security law on the former British colony on June 30, a move condemned by some foreign governments, business groups and rights groups. Hong Kong and authorities in Beijing said the law was necessary to restore stability after more than a year of anti-government protests. "Sitting in front…