Former Union Minister Virbhadra Singh has threatened to file defamation suit against those indulging in his character assassination. Criticizing BJP leader Arun Jaitley for making allegations of forgery, money laundering and income tax evasion against him, Singh said in Shimla wednesday that Jaitley should instead worry more about his national President who is facing allegations of dubious funding of his companies.The Himachal PCC chief said instead of raising political issues, they are casting personal allegations against him.