DAVID Hicks will seek to overturn his terrorism conviction and plans to sue the Australian government but former foreign minister Alexander Downer says Mr Hicks should be grateful he is still not in Guantanamo Bay.

Rejecting criticism of the Howard government after yesterday's US court decision to rule invalid the crime for which Mr Hicks was convicted, Mr Downer said he had no sympathy for Mr Hicks.

''He would have been there for years if it hadn't been for our intervention,'' he said.

''We very much used the close friendship with the US administration to get his case heard.